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LIBRARY OF CONGRESS. 



— dapjjrigljt If u- 



UNITED STATES OF AMERICA. 






A GUIDE 



Elementary Chemistry 



FOR BEGINNERS 



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Le ROY C; COOLEY, Ph.D., 

PROFESSOR OF PHYSICS AND CHEMISTRY IN VASSAR COLLEGE 



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Copyright, 1886, by 

IVISON, BLAKEMAN, TAYLOR, AND COMPANY 

NEW YORK AND CHICAGO 



PRESS OF HENRY H. CLARK & CO., BOSTON. 






PREFACE. 



In an Elementary Chemistry, written in 1872, it was my 
purpose to give a short course, for beginners, in which the 
experimental evidence, on which the most fundamental parts 
of the science rested, should take the place of minute details 
and advanced theoretical discussions, hoping in this way to 
encourage the study of chemistry by experiment instead of by 
books alone, as was so much the custom at that day. A Student's 
Guide, printed for the use of my classes in 1878, contained a 
course introductory to qualitative analysis, giving the student 
nothing but an outline of experiments. He was expected 
to make the experiments, to observe and describe his own 
results, and from these to construct for himself a plan for the 
detection of the metals. I now combine the leading ideas of 
those two books, and offer to my fellow-teachers a new volume, 
in which they are more fully developed in ways suggested by 
the unbroken experience of the intervening years. 

Chemistry as a branch of study in the schools has two great 
merits happily combined. One is to be found in the kind of 
knowledge it offers, and the other in the peculiar mental 
training it affords. Of these the latter is certainly not the 
least important, because a person is well educated, not so 
much in proportion to what he knows, as in proportion to 
what he can do with his knowledge. Hence a chief purpose 



iv PREFACE. 

of the study of elementary chemistry in schools is to educate 
the mind by giving it the right kind of exercise in the use of 
its powers. 

I have therefore tried to make a judicious selection of the 
most fundamental facts and principles of chemistry, and to 
present these in such a way that the student must constantly 
use his senses to discover facts, his reason in drawing correct 
inferences from the data he collects, and good English in ex- 
pressing accurately what he sees and thinks. 

I know 7 of but one way to teach a student how to acquire 
a real knowledge of nature, and that is, to fix his mind habit- 
ually on things and events brought under his own eye, and 
direct him to the discovery of facts and principles for himself. 
The use of apparatus is, of course, indispensable if the 
student is thus to study phenomena instead of descriptions 
of phenomena, and the use of apparatus, by himself, is with- 
out doubt the method which is most certain to stimulate his 
mind to the greatest activity. Laboratory study for students 
in high schools is rapidly growing in favor, but unfortunately, 
in many schools where chemistry is taught, the difficulties in 
the way of this method are still thought to be real. Even in 
these, chemistry to be truly useful should be presented as a 
study of phenomena, by experiments, instead of what some- 
body has said about phenomena in books. 

I have therefore tried to construct a course of experiments 
suited to the use of the beginner, at his laboratory desk, and 
to the use of the teacher for his class of beginners, where 
facilities for students to work for themselves seem to be out 
of reach. 

The study of any subject by experiment combines two kinds 
of exercise; mechanical and mental operations go hand in 
hand. On this account experimental investigation is a com- 



PREFACE. V 

plex and difficult work. All that can be done to make it less 
so. for beginners is to make one or the other, the mechanical 
or the mental processes, predominate in our elementary course 
of instruction. Then which shall it be? The mechanical of 
course stands first, in one sense, for there will be no phenomena 
to study until apparatus is selected and arranged to exhibit 
them. But, on the other hand, a wise selection of apparatus 
and conditions cannot be made by one who has not already 
acquired some skill in tracing the relations of cause and effect, 
and some experience in the application of experimental 
methods. I think we should first cultivate the power to 
observe exhaustively and to detect relations, — that we should 
make the mental more prominent than the mechanical in the 
elementary study of chemistry. Accordingly : 

In this course of experiments the mechanical operations 
are described in quite minute details. Exactly what is to be 
done is told, but what is to happen, and the meaning of it, is 
for a time withheld. Exceptions to this plan will be found 
in the description of processes which are simply means to 
secure conditions, and in the statement of facts which may be 
needed for immediate use. But in general the phenomena 
which hold the chemistry of substances or processes are left 
for the student to discover. See, for example, page 35, or 
pages 85, 86. 

I know that much stress is, by many, laid upon the industrial 
value of an instrument-making course in chemistry. But it 
seems to me that the study of chemistry is not primarily to 
teach mechanics, and that the use of tools and the possession 
of mechanical ingenuity can be better acquired in the indus- 
trial school or workshop, where these are the specific aims, 
than in the laboratory of the high school or academy, where 
the acquisition of knowledge for the sake of mental training is 



VI PEE FA CE. 

the chief purpose. Home-made apparatus is not to be de- 
spised, but to be greatly respected, where nothing better can be 
had, for much can be done with the most common utensils, 
such as bottles, fruit-jars, tea-saucers, and oyster-cans. But 
certainly beginners can do better work with good facilities. than 
with poor ones. And while there is so much in the market 
which is at once scientific and inexpensive, the student should 
be taught to reach more accurate results than are otherwise 
possible by the use of it. Productive ingenuity and skill 
must be founded on exact knowledge and clear thinking ; they 
cannot precede these. Therefore : 

The apparatus called for in this course has been selected 
from that which is made for, and approved by, chemists. The 
pieces are neat, simple, easily put together, always in market, 
and as cheap as possible for good scientific work. (See Appen- 
dix, Fig. 69.) 

A brief summary of the most important facts and principles 
follows the experimental work, by which the student can check 
and correct his results. In this summary will be found the 
information which should be acquired by beginners in chem- 
istry. I have tried to include in it only such things as will be 
of most value to the many who will finish the study of chem 
istry in the -high school, and to the few also who are there to 
lay a foundation for college work. " Not how much we know 
is the best question, but how we have got what we know, and 
what we can do with it, and, above all, what it has made of 
us." — J. P. Leslie. 

It is not well to undertake too much. It is not best to have 
the student's text-book burdened with matter which he is not 
expected to master. There is more education to be gained by 
extending the search for facts into other volumes than by 
skipping parts of the book in use. I have not given a long 



P HE FACE. vii 

list of experiments, but have tried to make a judicious selection, 
believing that a few typical ones well made and thoroughly 
studied, are far more useful than a larger number would be 
if studied in haste. What I mean by the thorough study of a 
few experiments in the treatment of a subject may be seen by 
referring to "Substitution," pp. 19-21 : " Decomposition of nitric 
acid," pp. 92-95; or " Chlorides," pp. 141-145. 

Additional work is better when provided by teachers for such 
pupils or classes as have time or talent to undertake it. I 
would make such work partake of the nature of research as 
much as possible. A student may be given some question to 
be answered by his own experiments, or two substances whose 
mutual reactions and results he is directed to investigate, or 
a single body whose properties he is asked to study and report. 
Some work of this kind I have given under the head of "Ex- 
ercises." (See, for examples, pp. 39, 82, 100.) 

Next in value to research in the laboratory stands research 
in the library. By all means teach the student how to make 
the results of his study, with apparatus and the text-book, the 
nucleus around which to group other facts, a center from 
which to extend his knowledge. From the following works 
the teacher can select abundant materials for this exercise, in 
kind and quantity suited to the varying wants of different 
individuals or of successive classes. Buckley's "Short History 
of Natural Science." Wurtz' " History of Chemical Theory." 
Wurtz' "Atomic Theory." Cooley's "New Text-Book of 
Chemistry." Cooke's "New Chemistry." Remsen's "Or- 
ganic Chemistry." Remsen's " Theoretical Chemistry." Ros- 
coe and Schorlemmer's " Treatise on Chemistry." Fresenius' 
"Qualitative Analysis." Douglas and Prescott's "Qualitative 
Analysis." 



Vlll PREFACE. 

I have in all cases rejected dangerous experiments, but I 
have in many cases devised simple, safe, and efficient ways to 
study explosive and noxious substances. See, for examples, 
Hydrogen, pp. 29, 30, and Chlorine, pp. 138, 139. 

The wood-cuts which represent the experiments are, with 

a single exception, Fig. 23, made from the photographs or 

drawings of the apparatus in actual use. For the selected cuts, 

which illustrate the descriptions of historical or industrial 

work, I am unable to give the credit which is due to their 

unknown authors. 

L. C. C. 

POUGHKEEPSIE, June, 1886. 



CONTENTS. 



OBSERVATION AND EXPERIMENT. 

PAGE 

Chemistry : Observation ; experiment ; way to study . . 9 

CHEMICAL CHANGES. 

Decomposition ; combination ; substitution ; double decom- 
position ; heat and chemical action ; electricity and 
chemical action; light and chemical action .... 13 

Hydrogen: Preparation of; properties of; cause of the 
explosion of; water a product of its combustion; heat a 
product of its combustion 28 

Oxygen: Preparation of ; properties of; chemical actions 
of; occurrence of; allotropism of; ozone 33 

Exercises : Experimental study of chemical changes . . 39 

CHEMISTRY OF COMBUSTION. 

Burning of a candle ; burning of other substances ; material 
products; heat also a product; light also a product; 
structure of flame ; queries 41 

CHEMISTRY OP WATER. 

Analysis and synthesis ; analysis of water ; composition of 
water by weight ; percentage composition ; composition 
by volume; constant composition of water; constant 
composition of other compounds ; the law of constant 
composition ; water in nature ; solvent power of water ; 
drinking waters; mineral waters; effect of cold on 
water . . 50 

Exercises : Experimental investigations 63 

is 



X CONTENTS. 

CHEMISTRY OF THE ATMOSPHERE. 

PAGE 

Lavoisier's experiment; oxygen removed from air by sul- 
phur and by phosphorus 65 

Nitrogen: Preparation of; properties of; Am: analysis 
of; composition of; a mixture; diffusion of gases . . . 66 

Respiration : Of animals ; produces changes in air ; 
ventilation ; of plants 77 

Exercises : Investigations — the action of sulphuric on 
oxalic acid and the action of phosphorus on air ... 82 

COMPOUNDS OF NITROGEN, HYDROGEN, AND OXYGEN. 

Office of nitrogen in the air; character of the compounds 
of nitrogen . . 84 

Animonia: Production of ammonia; the nascent state; 
ammonia in gas-works ; preparation of ammonia ; prop- 
erties of ammonia; its action on the acids: composition 
by volume 84 

Nitric Acid: Occurrence of, in nature; made from 
sodium nitrate; properties of; decomposition of; the 
nitrates 90 

Nitrogen Oxides : Study of the decomposition of nitric 
acid by copper; proof that air takes part in the action; 
the several products; nitrous oxide; five nitrogen 
oxides ; the law of multiple proportions ; combining 
weights 92 

Exercises : Investigation of tests 98 

THE COMPOSITION OF PLANTS. 

Decomposition of wood by heat ; constituents of plants . . 101 

Carbon: Source of carbon in plants; charcoal-making; 
lamp-black ; action of charcoal on gases ; action of 
charcoal on colors ; action of charcoal on oxides ; the 
diamond ; graphite ; allotropism of carbon 103 



CONTENTS. XI 

PAGE 

Carbon dioxide: Preparation of; properties of; carbon 
monoxide; compounds of carbon and hydrogen; 
methane 112 

ELEMENTS, MOLECULES, AND ATOMS. 

The number of the elements; table of names, symbols, 
and atomic weights ; three forms of matter ; facts, laws, 
and theories, to be carefully distinguished. Mole- 
cules; some facts about the expansion of gases; the 
theory; chemical changes are changes in molecules; 
atoms; "multiple proportions" explained; atomic 
theory ; symbols ; formulas ; atomic weights ; molecular 
weights ; reactions 117 

ACIDS, BASES, AND SALTS. 

Acids; salts; hydroxides; reaction of acids and bases; 
neutral compounds 129 

Chemical names : Of acids ; of salts ; of bases .... 135 

CHLORINE AND THE CHLORIDES. 
Discovery of chlorine; preparation and properties of 
chlorine ; bleaching ; the chlorides ; chlorides by 
chlorine water ; chlorides by hydrochloric acid ; chlorides 
by aqua regia ; two chlorides of one metal ; hydrogen 
chloride: Preparation of; composition of; comparison 
of volume ; composition of compounds ; the " two-vol- 
ume " law deduced; test for chlorine and the chlorides . 138 

The Chlorine Group : Bromine ; iodine ; fluorine ; 
their hydrogen compounds ; relation of atomic weights 
to properties 147 

Exercises : Study of tests 151 

SULPHUR AND ITS COMPOUNDS. 

Native sulphur and sulphides ; preparation of sulphur ; 
properties of sulphur ; artificial sulphides ; hydrogen 
sulphide : preparation and properties of; use of . , . 154 



xii CONTENTS. 

PAGE 

The Sulphur Group: Selenium; tellurium; hydrogen 
compounds; general behavior; relation of atomic 
weights to properties 10 1 

Sulphurous Oxide and Acid : Preparation of sulphur- 
ous oxide; properties of sulphurous oxide; sulphurous 
acid; bleaching 163 

Sulphuric Acid and the Sulphates: Properties of 
the acid ; uses of the acid ; test for the acid ; manufac- 
ture of the acid ; the sulphates : sulphates by action 
of the acid on metals ; by action of the acid on bases ; 
two sulphates of the same metal ; other sulphur acids . 166 

Exercises : Investigation of tests 173 

PHOSPHORUS, AND THE NITROGEN GROUP. 

Discovery of phosphorus; properties; red phosphorus; 
matches ; phosphorus oxides and acids ; the phosphates ; 
manufacture of phosphorus 175 

Arsenic : Arsenous oxide ; arsenic oxide ; arsenic and 
hydrogen; Marsh's test 178 

The Nitrogen Group : Members ; their hydrogen com- 
pounds; relation of atomic weights to properties . . 182 

SILICON, AND THE CARBON GROUP. 

Silicon : Its oxide ; the carbon group : members ; their 
hydrogen compounds; their oxygen compounds; the 
silicates 183 

Boron : The element ; borax ; boric acid ; no hydrogen 
compound 185 

VALENCE. 
A difference in atoms; valence defined; substitution 
governed by valence; the valence of boron; valence 
useful in study of reactions ; valence of an element 
changes . . r 188 



CONTENTS. xm 

THE METALS. 

PAGE 

What is a metal ? number and abundance of the metals ; 
occurrence in nature 192 

THE POTASSIUM GROUP. 

Potassium: Description of; chemical action on water; 
occurrence in nature ; potassium carbonate ; potassium 
hydroxide; experiments in the preparation of some 
other salts ; flame test 195 

Sodium: Description of; occurrence in nature; sodium 
carbonate; sodium hydroxide; flame test; study of 
reaction of sodium compounds 199 

Ammonium: Facts about ammonia; comparison of 
formulas; the hypothetical metal; its salts; the sul- 
phides ; study of reactions of ammonium compounds . 201 

The Potassium Group : Names of members ; compari- 
son of properties 204 

THE CALCIUM GROUP. 

Calcium: The metal; its occurrence in nature; effect of 
heat on the carbonate ; effect of acids on the carbonate ; 
effect of water on the carbonate ; the sulphate ; to pre- 
pare the insoluble compounds ; to prepare the soluble 
compounds 206 

The Calcium Group: Names of the members; com- 
parison of atomic weights and properties ; study of 
characteristic reactions; flame colors 210 

METALS OF THE ZINC GROUP. 

Magnesium : The metal ; its compounds ; study of reac- 
tions of magnesium compounds 212 

Zinc: The metal; manufacture of; uses of; compounds 
of; preparation of insoluble compounds, and study of 
characteristic reactions ; the zinc group 212 



XIV CONTENTS. 

THE IRON GROUP. 

PAGE 

Manganese: The metal; its oxides; the potassium man- 
ganate and permanganate ; study of reactions with 
manganese salts; cobalt; nickel 217 

Iron : Occurrence of iron ; its ores ; roasting and reducing 
the ores ; cast-iron ; the three forms of iron ; manufac- 
ture of wrought-iron ; manufacture of steel, Bessemer 
process ; cementation ; compounds of iron ; two classes ; 
the two chlorides; distinctive reactions for the two 
classes ; general reactions of iron salts 220 

Chromium: The metal ; its ore ; the potassium chromate ; 
the dichromate ; reactions of chromium salts .... 229 

The Iron Group : comparison of properties 231 

ALUMINUM. 

The metal; alum; aluminum oxide; study of reactions 
of aluminum salts 233 

THE ANTIMONY GROUP. 

Antimony: The metal; alloys of;, bismuth; the anti- 
mony group ; the reactions of arsenic, antimony, and 
bismuth compared 235 

TIN AND LEAD. 

Tin: Occurrence in nature; extraction from the ore; 
properties of the metal ; compounds of tin ; distinctive 
reaction for ous and ic compounds ; general reactions of 
the salts of tin 239 

Lead: Occurrence in nature; extraction from the ore; 
two methods ; lead oxides ; lead carbonate ; reactions of 
the salts of lead 242 

THE COPPER GROUP. 

Copper : Occurrence in nature ; extraction from its ores ; 
properties of the metal ; copper compounds ; the sul- 
phate ; study of reactions of the salts of copper . . . 247 



CONTENTS. XV 

PAGE 

Mercury: Occurrence 1 in nature; extraction from its ore; 
properties of the metal ; compounds of mercury ; the 
two chlorides ; mercurous compounds ; mercuric com- 
pounds ; study of reactions 251 

Silver: Occurrence in nature; extraction from its sul- 
phide; extraction from galena; properties of the metal; 
compounds of silver ; reactions of the salts of silver . . 254 

GOLD AND PLATINUM. 

Gold: Occurrence in nature; obtained by " washing "; 

obtained by " amalgamation " ; properties of gold . . 259 
Platinum: Occurrence in nature; properties of the 

metal; the platinum group 260 

CLASSIFICATION. 

Classes: How they are made; the classes of the non- 
metals founded on valence; metals not always classed 
in this way ; more than one way to group the metals ; 
four principal w r ays to classify the metals 262 

The Natural System: Classification by atomic weights; 
Newland's discovery; Mendelej eft's extension; the spiral 
of elements ; the vacant places 264 

The Analytical System : Classification founded on solu- 
bilities ; analytical table drawn from the preceding ex- 
periments in this course ; how to find out what metal a 
compound contains ; making notes ; to identify the acid 
part; to name the salt; hint for further work; form 
of notes 268 



ELEMENTARY CHEMISTRY. 



OBSERVATION A]STD EXPERBIEXT. 

Ix the study of Chemistry we are to learn some things 
about the different kinds of matter. There are two ways 
in which these things have been found out, and in these 
same ways we can most easily learn what these things are. 
These two ways of studying nature are called observation 
and experiment. 

Observation. — When I look at something which is 
going on, and watch carefully to see what happens, my act 
is an observation. To look at an object so closely that we 
can see its shape, its color, and whatever else is visible 
about it, is an act of observation. 

If, for example, I desire to know as much as possible 
about a butterfly, the best way to learn it is to catch the 
butterfly, look at it intently, note down and remember 
what I see. The butterfly would show me that it has four 
wings, six legs, two long hair-like bodies (antennae) reach- 
ing forward from its head with knobs upon their ends, two 
large, dark, and prominent eyes which do not close nor 
turn, and that the beautiful colors of its wings are clue to 
a fine dust which is easily rubbed off by my fingers. All 
these facts I could learn by holding the insect in the hand 
and looking at it thoughtfully. 

Knowledge which I get in this way is learned by obser- 
vation. 



10 



OBSERVATION AND EXPERIMENT. 



Experiment. — But if, instead of only looking at an 
object as I find it, I do something to it to see how it will 
behave or appear in different conditions, this operation is 
an experiment. 

Will 5 cubic centimeters of water dissolve as much as 10 
grams of granulated sugar ? I cannot find out by simply 
looking at sugar and water. In order to learn what the 
fact is, I may put the two things together in the right 
way, and if I do so I make an experiment. Thus: 

Ex. 1. — I take a tall glass cylinder, a, Fig. 1, which is 
graduated to measure cubic centimeters, and pour in water 




Fig. 1. 

up to the 5 cc. mark. 1 I transfer this water to one of 
the thin round-bottomed cylinders, Z>, called a test-tube. 
I also weigh out 10 g. of granulated sugar 2 and put it 
into the water in the tube b. s I now warm the tube in the 
flame of a Bunsen lamp, c. There is danger of breaking 
the tube if I heat it too suddenly, or too long in one spot, 

1 If one must get along without a graduated cylinder, he may 
obtain 5 cc. very nearly by filling his test-tube one inch above the 
rounded bottom. The tube is supposed to be f inch in diameter. 

2 If one must get along without a balance, he can obtain about 
10 g. of dry sugar by rilling a teaspoon twice. 

3 Fold a narrow strip of paper into the shape of a trough and lay 
this in the tube, which should be held in a slanting position. The dry 
sugar will slide safely down this trough instead of clinging to the wet 
walls of the tube. 



OBSERVATION AND EXPERIMENT. 11 

and to avoid this danger I move it slowly in the flame to 
heat all sides evenly. When the liquid begins to boil I lift 
the tube into the hot air above the flame, where I can keep 
it hot without boiling it too vigorously. I watch to see 

Whether the sugar remains, or becomes less and less. 

Whether it all finally disappears. 

If the liquid at length becomes, as it will, almost or 
quite transparent, we shall know that 5 cc. of hot water can 
dissolve 10 g. of sugar. I will then stand the tnbe in the 
tnbe-rack, and when it is cold I will look again and see 

Whether 5 cc. of cold water can hold the 10 g. in solution. 

Let us keep this syrup for use in another experiment. 

The sap of some trees and the juices of some plants are 
natural solutions of sugar in water, but 
the quantity of sugar in 5 cc. of these 
juices is very small. Nothing but an 
experiment could have first shown that 
5 cc. of water can dissolve so much 
sugar as we have found it to do. 

But in experiments we often put 
things together in ways in which na- 
ture never does. For example, I wish 
to know how sugar will behave in strong sulphuric acid. 
Nature never puts these two things together, and the only 
way I can find out how they will act in the presence of 
each other is to bring them together. Thus : 

Ex. 2. — I measure out 5 cc. of strong sulphuric acid 
with the cylinder a, Fig. 1, pour it into an empty test-tube, 
then rinse the cylinder and stand it on a small plate, Fig. 2. 
I now pour the sugar syrup made in the other experiment 
into this cylinder. I am ready now to bring the two to- 
gether. I pour the acid in a slender stream into the syrup, 
and watch for every change that happens. I notice 

A change in color. 




12 OBSERVATION AND EXPERIMENT. 

A change in volume (size). 

A change in temperature (warmer or colder). 

A new substance unlike sugar or syrup or acid. 

As soon as the experiment is over I write, in my note- 
book, a short account of what I did, and the results just as 
I saw them. 

The fact is that a coal-black, bulky mass of hot carbon 
or charcoal is the result of bringing these two substances 
together. 

The science of Chemistry is founded on facts which have 
been discovered by experiment, and the most natural way 
to study Chemistry is by the same means. The best way for 
the student is to make the experiments himself. The sec- 
ond best way is to see them made by a teacher. In either 
case the student should remember that the object of mak- 
ing experiments is to discover truth. An experiment may 
be pretty and interesting, but its value does not lie in its 
beauty. No experiment is good for anything in the study 
of Chemistry unless it helps to reveal some truth. 

The student should remember, also, that it is not what he 
reads about experiments, or hears a teacher say about them, 
that is going to give him the best and quickest insight into 
Chemistry, but that which he sees with his own eyes and 
describes in his own words. 

To study Chemistry by experiment the student should 
obey the following rules : — 

1. Arrange the apparatus and use it exactly as directed. 

2. Watch carefully to see every change which takes place. 

3. Note accurately on paper every important change. 

4. Compare these results with the facts stated in the 
book, and correct those which are found to be wrong. 

5. Study carefully to see how certain inferences may be 
made from the results. 



CHEMICAL CHANGES. 



We already know by observation that there are changes 
all the time going on in bodies of matter. Some things 
change very rapidly, others very slowly. Wood changes 
to smoke and ash sometimes in a few minutes ; a stone 
crumbles to powder only after many years. But nothing 
can forever stay exactly as it is. 

The first thing we have to do in Chemistry is to become 
acquainted with these changes. How do they differ? How 
are they brought about, and what terms are used to de- 
scribe them ? 

Ex. 3. — I take a piece of magnesium wire or ribbon 
about six inches long, grasp one end with a pair of pincers, 1 
and hold the other end for a moment in the flame of the 
Bunsen lamp, Fig. 3. I see that 

The metal becomes red hot, then bursts into flame. 

Nothing finally remains but a crumbling white solid. 

Ex. 4- — I now i n 
the same way hold a 
piece of iron wire in 
the flame of the Bun- 
sen lamp, and see that 

The metal becomes red hot, but 
does not burn. 

And finally, when cold, is the 
same substance as at first. 

Both metals were changed by 
the heat, but in very different 
ways. The iron became hot in- "Wi~ 

1 A homely handle can be made by starting a split in one end of a 
stick. The wire can be inserted in the split and held as with pincers. 




14 CHEMICAL CHANGES. 

stead of cold, red instead of black, but it remained iron. 
The magnesium did not remain magnesium, but was changed 
into a new substance ; the crumbling white solid is a very 
different thing from the tough, gray, and lustrous metal. 
There was no change in the substance of the iron; there 
was a change in the substance of the magnesium. 

Observations. — I watch the clouds and see them 
change in size and shape, and oftentimes in color. But 
their substance does not change, for clouds are made of 
water-vapor, whatever may be their sizes, shapes, or colors. 
To-day a piece of iron is smooth and bright, but if left in 
moist air it will in time be found covered with iron-rust. 
A part of the iron becomes changed into this very different 
kind of matter. 

Further observations show that there are changes going 
on all the time around us which do not alter the 
nature of substances, like the changes in the iron 
wire when heated. All such changes are called 
physical changes. There are others in which 
the substance of bodies is changed into matter 
of a different kind, like the burning of the 
magnesium. All such changes are called chem- 
ical changes. And so we learn that the multi- 
tudes of changes in the world of matter may be 
grouped in two great classes. 

If now we go on to compare one chemical change with 
another we shall find that there are several different 
varieties. 

Decomposition. Ex. 5. — I put one gram of " red oxide 
of mercury 7 ' into a side-neck ignition-tube, 1 Fig. 4, — just 

1 Ignition-tubes are made of "hard" glass while other tubes are 
made of " soft" glass. Hard glass will stand a strong heat, while soft 
glass will not. Common test-tubes may be used for heating liquids ; 
ignition-tubes should be used for heating dry solids. 




CHEMICAL CHANGES. 



15 




about enough to till the rounded bottom. I close the mouth 

of the tube with a nicely fitting cork, and slip one end of 

a piece of rubber tubing, e, Fig. 5, over the end of the 

side-neck. I then fix the 

tube very obliquely in the 

clamp of the support, f. 

I next put a half -inch of 

water into the test-tube b, 

and slip the free end of the 

rubber tube down into it. 

The oxide is now ready 
to be heated, and if any- 
thing shall be driven out 
we may catch it in the Fig 5 

test-tube. 

I now apply the flame of the lamp, and move it slowly 
to heat the bottom of the tube evenly. The upper part of 
the tube must not be heated. Now look for and describe 

A change in the color of the oxide. 

A coating which forms on the cold walls of the tube. 

Bubbles which escape from the rubber pipe in the water. 

A change in the quantity of the oxide. 

Were the bubbles which came over through the water 
anything more than air ? To answer this question I take 
a splinter of wood, very slender, and long enough to reach 
to the bottom of the tube, set fire to one end and watch 
the spark very closely while I push it to the bottom of the 
tube to see 

Whether it burns just as it does in air. 

The Facts. — By heating the red oxide of mercury it is 
first blackened and then broken into two kinds of matter 
quite unlike itself. One of these appears in shining drop- 
lets on the cold walls of the tube, the other goes off as a 



16 CHEMICAL CHANGES. 

colorless gas which brightens the burning of a splinter. 
The shining droplets which coat the cold walls of the tube 
are mercury, and the gas in which a splinter burns with 
unusual brightness is oxygen. 

This is a line example of chemical change. But the most 
important thing to notice is, that in this change one sub- 
stance is broken into two which are entirely unlike itself 
and unlike each other. Such a chemical change is called 
decomi^osltlon. 

Decomposition of Potassium Chlorate. Ex. 6. — Po- 
tassium chlorate is a white solid. Before I heat it the 
coarse grains or crystals should be reduced to powder: I 
grind it in a mortar (Fig. 6). I put two 
grams of the powder into the ignition- 
tube, 1 Fig. 4. This quantity will fill 
about one inch of the tube. I put three 
\ or four cubic centimeters of blue litmus 
solution into one test-tube, b, and as much 
lime-water into a second tube, c, Fig. 5, 
and provide a good cork for each. I put the end of the 
rubber tube into the litmus, and then heat the chlorate just 
as I did the red oxide before. Watch for and describe 

The changes in the chlorate. 

The bubbles from the pipe in the litmus. 

After a while I put a match-flame into the mouth of 
the tube and see that it burns with unusual brightness. 
This shows that the tube is filled with oxygen. 

I then put the end of the rubber tube over into the lime- 
water in c, and close b with its cork, in order to keep its 
oxygen for use further on. 

At length the boiling chlorate thickens, and soon after 

1 The tube must be clean and dry. A piece of dry cloth, or a sponge 
tied on the end of a wire or stick, is convenient for wiping tubes. 




CHEMICAL CHANGES. 17 

dries up completely to a white solid. The work is done. 
I stop the heat, remove the rubber tube, and cork the test- 
tube c, to keep its oxygen also for future use. 

Has any change been made in the litmus or the lime- 
water ? 

The Facts. — By heating potassium chlorate it is first 

' melted and afterward broken into two substances, unlike 

itself and each other. One is the white solid, left in the 

ignition-tube, and the other is oxygen. The chlorate is 

decomposed. 

Oxygen, which has appeared in both these experiments, 
is an important substance, and as soon as we are through 
with the special study of chemical changes we will examine 
it fully. At present We will make two experiments with it. 

Combination. — What will happen if a bit of coal is 
heated in oxygen ? 

Ex. 7. — I wind the end of a small wire around a little 
splinter of charcoal, heat the charcoal until it holds a spark 
of fire, and then lower it into the oxygen in the test-tube c, 
Fig. 5, over lime-water. Notice 

What effect is produced on the spark. 

Whether the charcoal wastes away. 

Will the oxygen brighten a match-flame afterwards ? 

I now cover the mouth of the tube with my finger and 
shake it briskly. 

What change takes place in the lime-water ? 

The Facts. — Charcoal with a dull red spark will glow 
brightly in oxygen and burn away rapidly ; the oxygen is 
used up at the same time, and the lime-water afterward 
becomes turbid and white. 

But we know that oxygen will not whiten lime-water : 
this was proved in Ex. 6. (How was it proved ?) Charcoal 
also will not whiten lime-water. But the burning of the 



18 CHEMICAL CHANGES. 

charcoal in oxygen yields something which will. It is a col- 
orless gas called carbon dioxide. In place of charcoal and 
oxygen we have carbon dioxide, which is very unlike both. 
Now the thing most important to see in this case is that 
two substances are changed into one. 

Ex. 8. — I take a piece of wire, — perhaps a knitting- 
needle, — warm it a little, and then plunge it into some 
flowers of sulphur. A thin layer of sulphur will cling to 
the wire. I set fire to this sulphur, and then at once thrust 
it into the test-tube b, containing oxygen and litmus, left 
from Ex. 6. Notice and describe 

The fine color of the flame. 

The vapor which is produced. 

I next close the tube with my finger and shake it to mix 
the vapor with the litmus. 

What change is made in the color of the litmus ? 

Sulphur burns more freely in oxygen than in air, and 
with a rich blue flame, filling the vessel with white vapor. 
This vapor mixed with blue litmus solution changes the 
color from blue to red. In place of the sulphur and oxy- 
gen, both of which are used up, we have a new substance 
quite different from either. This new substance into which 
sulphur and oxygen are changed is called sutyhiir dioxide. 

Now this change is like the change when the charcoal 
was burned. It is another case in which two substances are 
changed into one. Such a chemical change is called combi- 
nation. 

Decomposition or Combination? — When ammonia 
and hydrochloric acid are mixed a chemical change occurs ; 
is it a chemical decomposition or a chemical combination ? 

Ex. 9. — I put a cubic centimeter of strong ammonia 
water into a tube or bottle, rinse it around to wet the sides, 
and then pour it out. I put as much hydrochloric acid into 



CHEMICAL CHANGES. 19 

another similar vessel and treat it in the same way. By 
this means I till the vessels with the colorless vapor of the 
two substances. I next bring these two vessels 
month to month and hold them one above the other 
(^Fig. 7). Xotice and describe 

The change which the colorless vapors undergo. 
The two substances used are colorless, but a new 
one is made which is seen as a white cloudlike mass, 
which rolls down toward the bottom of the tube, 
and will roll back again if the tubes be inverted. 
In fact, the hydrochloric acid and ammonia com- 
bine to form one thing. — called ammonium chloride. Fi s- 7 - 

Substitution. — All chemical changes are either decom- 
positions or combinations. But in a great many cases the 
two kinds take place at once. This is true in the action of 
zinc and hydrochloric acid. 

Ex. 10. — I have a wide-mouth bottle which 
will hold 200 cc. and a square of glass or of 
heavy paper with which to cover it. 

Into the bottle I put two or three pieces of 
zinc, and just cover them with hydrochloric acid. 
I then close the bottle with its cap of glass or 
"nTT paper (Pig. 8). 
Describe the action which sets in. 
Feel the bottle, and what effect is discovered ? 
I now bring a match-flame to the mouth of the bottle 
while I lift the cover. 
Describe the result. 

A violent effervescence takes place whenever zinc and 
hydrochloric acid are brought together. The vessel is 
heated, and a gas escapes which takes fire with explosion. 
This gas is hydrogen. Heat and hydrogen are two products 
of the chemical action. Are there anv others ? 




20 



CHEMICAL CHANGES. 




Fig. 9. 



Ex. 11. — To answer this question I examine the liquid 
left in the bottle, when the bubbling of gas has come to an 
end. I must first filter the liquid to rid it of black flakes, 
which are only impurities of the zinc, and afterward 
( vaporate the liquid to recover any solid substance it may 
contain. 

1. Filtration. — Cut a square of filter paper, A, Fig. 9, 
about three inches on a side, — a little less than twice the 

length of the sloping side of 
a funnel, /. Fold the square 
into a triangle by bringing 
corners d and a together. 
Fold again, bringing corners 
c and b together, making the 
triangle B. 

Then trim the edges along 
the circular line e h. Open 

the triangle (leaving three thicknesses of paper on one side 

and one on the other), and we have a little 

paper funnel, C, which will fit neatly in 

the glass funnel, /. Press it in and wet 

it with water. Then rest the funnel on a 

test-tube and pour the liquid with its sedi- 
ment into it. The liquid will run through, 

but the sediment will stay on the filter. 

2. Evaporation. — Pour the clear 
liquid into a porcelain dish and heat 
it over a low flame, as shown in Fig. 
10. It may boil, but should do so 
very gently. The water will slowly 
pass away as vapor, but any solid substance which is dis- 
solved in it will stay in the dish. 

I will evaporate the liquid left in Ex. 10, and just fil- 
tered, down to about one-third its bulk, and then let it 




Fig. 10. 



CHEMICAL CHANGES. 21 

stand until it is cold. A brown solid is now seen, if the 
evaporation has gone far enough. This brown solid must 
have been made by the action of the zinc on the hydro- 
chloric acid in Ex. 10. It is called zinc chloride. 

We began the experiment with zinc and acid ; we after- 
wards find hydrogen, the brown solid, and heat, in place of 
these two substances. 

In all, we have now found three products of the chemical 
action of zinc and hydrochloric acid. They are heat, hydro- 
gen, and zinc chloride. 

Now hydrochloric acid is a compound of the two ele- 
ments hydrogen and chlorine, and the zinc just takes the 
place of the hydrogen in it. In fact, the zinc has decom- 
posed the hydrochloric acid and combined with the chlorine 
of that substance. The hydrogen was driven out as a gas, 
which burned quickly while the solid zinc chloride * stayed 
behind in solution. 

When one substance takes the place of another in a com- 
pound, as the zinc took the place of hydrogen in the acid, 
the action is called substitution. This is one of the most 
common kinds of chemical action. 

Double Decomposition. — It often happens that when 
two things are brought together both are decomposed. This 
is the case with silver nitrate and sodium chloride. 

Ex. 12. — I take a small crystal of silver nitrate and drop 
it into a test-tube with 5 cc. of water, and shake it until it 
is dissolved. In another test-tube I dissolve some common 
salt, which in chemistry is known as sodium chloride. I 
now add a drop or two of the solution of salt to the silver 
nitrate. After seeing, 

What happens to show that a chemical action occurs ? 
I go on adding the solution of salt carefully, drop by drop, 

1 The solid is called zinc chloride because it is made up of ziuc and 
chlorine. When pure it is nearly white. 



22 CHEMICAL CHANGES. 

watching to see whether still more of the new substance is 
made by each addition ; and that I may make no mistake 
about this I shake the tube each time vigorously, and then 
wait till the solid settles a little before I add the next 
drops. I do this until a drop of the liquid gives no more 
of the white solid, and stop with that drop. 

If by accident I do get in a drop more than this, I add a 
drop of silver nitrate solution. 

I then filter the mixture as in Ex. 11. The white solid 
will be left on the filter-paper while a clear liquid will run 
through. 

I next evaporate this clear liquid, as shown in Fig. 10, 
until but little is left, and then, when it cools, crystals 
will appear. The new white solid is silver chloride, and 
the crystals are sodium nitrate. 

The silver nitrate and sodium chloride decompose each 
other, and then the silver and sodium just change places 
and form the two new compounds named above. The 
names themselves show this double change, thus : silver 
nitrate and sodium chloride become sodium nitrate and 
silver chloride. 

In all such cases as this, in which two substances decom- 
pose one another and form two new ones, the action is 
called double decomposition. We shall find another exam- 
ple of double decomposition in the action of mercuric 
chloride and potassium iodide. 

Ex. IS. — I take enough mercuric chloride in powder 
to half-way fill the rounded bottom of a test-tube, cover 
it with 5 cc. of water, and warm it until it is dissolved. 
I take about twice as much potassium iodide in another 
tube and dissolve it also in water. I put about 3 50 cc. 
of water into a wide-mouth bottle, and add the mercuric 
chloride solution. I now put in about one-half the solu- 
tion of potassium iodide, little by little. 



CHEMICAL CHANGES. 23 

Describe the result as it first appears. 
And the curious change which soon occurs. 

I go on adding the iodide, carefully noticing whether still 
more of the new substance is made by each addition, and, 
that I need make no mistake, I wait each time to let the 
solid settle a little and the liquid clear before I add the 
next drops. I do this until a drop of the iodide gives no 
more of the colored solid, and stop with that drop. If by 
accident I do get in too much, I will add drops of mercuric 
chloride until the last drop has no effect. The scarlet solid 
will soon settle and leave a clear liquid above it. 

We find that when mercuric chloride and potassium 
iodide are brought together in solution they yield a sub- 
stance whose color, at first bright yellow, very soon changes 
to a fine scarlet. The potassium iodide will give this sub- 
stance just as long as there is any mercuric chloride in the 
solution. When a drop fails, we may know that the chlo- 
ride is all used up. The scarlet precipitate (as we call a 
solid which comes by putting two liquids together) and 
a solid substance which stays dissolved in the water are 
the two new things into which the chloride and iodide 
were changed. 

ISTow the chemists tell us that mercuric chloride contains 
mercury and chlorine, and that potassium iodide contains 
potassium and iodine. When we put these two liquids to- 
gether the chlorine and iodine changed places. Our scar- 
let solid contains the mercury and iodine, and our white 
solid contains the potassium and chlorine. In fact, both of 
the old substances were decomjiosed, and the two new ones 
were made by their parts combining in different pairs. 

Suggestion to the Student. — Xotice all along how the 
name of a substance tells us also the names of the simpler sub- 
stances in it. When we see the name mercuric chloride we may 
be reminded of the names of its parts, mercury and chlorine ; and 



24 CHEMICAL CHANGES. 

in the same way potassium iodide suggests its parts, potassium 
and iodine. So, too, our yellow solid made of mercury and iodine 
is named mercuric iodide. 

Definitions. — A substance which is made up of two or 
more kinds of matter quite unlike itself is called a com- 
pound. Mercuric oxide is a compound of mercury and 
oxygen. For the proof of this see Ex. 5. 

The different kinds of matter of which a substance is 
made are called its constituents. Mercury and oxygen are 
the constituents of mercuric oxide ; sulphur and oxygen, of 
sulphur dioxide (Ex. 8). 

By far the larger number of substances are compounds ; 
but there are a few which have never yet been decomposed, 
and such are called elements. Mercury, oxygen, and sul- 
phur are examples of elements. Some seventy of these 
are now known, and out of this small number all the com- 
pounds in nature are made. 

But compounds rarely occur pure. Substances are min- 
gled together tw r o or more so completely that they seem 
to be only one, and yet each still has all its properties 
unchanged. Syrup of sugar is an example. The sugar and 
the water are simply mixed together without change of 
properties. Such substances are called mixtures. Brine is 
another example. 

All substances are either elements, compounds, or mix- 
tures. 

There are two ways of finding out what the constituents 
of a compound are ; one is analysis, the other synthesis. 
Any process in which we decompose a substance so as to 
learn what it is made of is an analysis. Ex. 5 was an 
analysis of mercuric oxide. Any process in which we 
make a compound by putting its constituents together is a 
synthesis. Ex. 8 was a synthesis of sulphur dioxide, and 
in Ex. 7 we found that carbon dioxide is composed of car- 



CHEMICAL CHANGES. 25 

bon and oxygen by making these two elements combine. 
This also was an example of synthesis. 

Heat and Chemical Action. — Heat is very often pro- 
duced by chemical changes. It was so in Ex. 10. It is so, 
for another example, in the case of 

Sulphuric Acid and Water. — Ex. llf. Into a wide- 
mouth bottle I pour 40 cc. of cold water, and provide a rod 
of glass, or of wood, with which to stir it. I then pour into 
it gradually, while I stir it, 40 cc. of strong sulphuric acid. 1 
Note the evidence that heat is produced as shown 

By handling the bottle. 

By inserting a test-tube holding a little alcohol. 

These chemical changes need no extra heat to start them, 
but yield heat as one of the products of the action. 

There are other cases in which heat must be used to start 
the change (Ex. 7 and Ex. 8), which once started produces 
heat enough, and often more than enough, to keep the 
action going. We touch the wood with a match-flame to 
start a fire, but once begun the burning is kept up by the 
heat of the chemical action itself. 

There are still other cases in which heat must be applied, 
not only to start the action, but also to keep it going (Ex. 5 
and Ex. 6). In these cases heat is not produced, but ab- 
sorbed, by the chemical action. 

The fact is that every chemical action is a source of heat 
or cold ; every change in the nature of a substance is accom- 
panied by a change in temperature. 

Electricity and Chemical Action. — We are told in 
the study of Physics, that if a strip of amalgamated zinc 
and another of copper are put into a vessel of very dilute 
acid they will yield a current of electricity. 

1 The heat would be stronger if the water were poured into the acid. 
This should never be done. Whenever strong sulphuric acid and water 
are to be mixed always pour the acid gradually into the water while 
you stir it. 



26 



CHEMICAL CHANGES. 




Ex. 15. — I first make a little zinc-copper couple in this 
way : I cut from a sheet of zinc, such as is used under 
stoves, a strip four inches long by one-half inch in width 
and bend it squarely at three-fourths inch from one end, z, 
Fig. 11. I then amalgamate it. For this I take a few 
cubic centimeters of the half-strong acid which was made 

in Ex. 14, and add to 
it five times as much 
water in a saucer. I 
must also have a little 
mercury in a test-tube. 
I first wet the zinc 
with the acid. I next 
pour the mercury first 
upon one side, then upon the other, and rub the whole sur- 
face gently with a piece of cloth. The surface of the zinc 
should now shine like silver ; it is amalgamated. 

I next take a piece of sheet-copper as wide as the zinc 
and two and a half inches long, and fold one end, as shown 
at c. I press the end of z into this fold and make the two 
fit closely by pressing the fold carefully (not to break the 
zinc) with pincers. The upright part of c is about two 
inches long and stands facing the upright part of £, as 
shown at a, Fig. 11. 

To prepare the dilute acid : I measure into the water-pan 
p water enough to be a little deeper than the copper c is 
high, and then add one-twentieth as much strong sulphuric 
acid. 

I shall also need a test-tube : to have it ready I lay one 
in the water, let it fill and sink. 

These preparations all made, I next stand the zinc-copper 
in the acid water. 

A torrent of bubbles rise alongside the copper. What 
are these bubbles ? To catch them I lift the test-tube, 



CHEMICAL CHANGES. 27 

bottom upward, letting no air enter it, and bring its mouth 
over the top of the copper, as shown at b. The bubbles 

now rise into the tube, driving the water out at the rate of 
1 cc. a minute, if everything works well. When the tube is 
about half filled with gas I light a match, and lift the tube 
slowly ; the Avater falls out, air takes its place, and as the 
flame touches the mouth of the tube a sharp report occurs, 
which says — hydrogen ! 

The acid water is decomposed and hydrogen is set free. 
But amalgamated zinc alone will not decompose the acid 
(try it), nor will copper alone (try it). Is there anything, 
more than zinc and copper, when they are together in the 
acid? Yes, there is, as we are told, the current of elec- 
tricity. The zinc-copper is a source of electricity, and the 
hydrogen is set free by the action of electricity. 

It is found that a great many chemical changes can be 
made by means of electricity. And, on the other hand, a 
great many chemical changes produce electricity. Like 
heat, electricity is sometimes an agent and sometimes a 
product in chemical action. 

Light and Chemical Action. — Light is also a product 
of chemical action. The light of our fires and the light of 
our oil and gas lamps are examples. Eemember, also, the 
burning of sulphur in Ex. 8, and of charcoal in Ex. 7. 

Light will also sometimes iiroduce chemical changes. 

Ex. 16. — I first make some silver chloride by filling 
a test-tube three-fourths full of water, adding a small crys- 
tal of silver nitrate, shaking until the crystal is dissolved, 
and then adding hydrochloric acid drop by drop. The white 
cloud which rolls down is silver chloride. I now place the 
tube in strong sunlight. 

What change occurs in the color of the chloride ? 

The change in color slowly from white to dark purple is 



28 



CHEMICAL CHANGES. 



a sign that a new substance is being made. In fact, light 
decomposes the silver chloride. For other examples, and 
for the explanation of this one, we must wait. 

Heat, light, and electricity are agents which Ave can use 
to bring about chemical actions which in their absence will 
not occur. 

Heat, light, and electricity are also products of chemical 
action. They are just as important to the chemist as are 
the material products, that is, the new substances, obtained 
at the same time. 

We now go on to examine hydrogen and oxygen gases 
which we have met with in several experiments. 



~~ ~ — 



Fig. 12. 



HYDROGEN. 

Hydrogen may be made by zinc and hydrochloric acid, as 
it was in Ex. 10. We may make and catch it as follows : 

Ex. 17. — I make enough dilute hydrochloric acid — one 
measure of strong acid to two 
measures of water — to fill the 
water-pan about two inches deep. 
I take the graduated cylinder, lay 
it in the acid, as shown in Fig. 12, 
and when it is thus filled with the liquid I lift it bottom 
upward and let it stand mouth down 
on the bottom of the pan, as in Fig. 
13. I next drop a piece of granu- 
lated zinc into the pan, and then 
carry the mouth of the cylinder over 
it. In all this work I use great care 
to not let a bubble of air get into 
the cylinder. The hydrogen bubbles 
form on the zinc, rise in the cylin- Fig. 13. 

der, and push the water down out of it, as shown in Fig. 14, 
until finally the cylinder is filled with hydrogen. 




CHEMICAL CHANGES. 



29 







Fig. 14. 



To Discover the Properties of Hydrogen 1 test 

the- gas by lighting a match, then lifting the cylinder out 

of the liquid rather slowly, month 

still downward, and then quickly 

bringing the flame to the open 

month. The gas takes fire with a 

dull report. Compare this result 

with that in Ex. 10. 

Ex. 18. — I fill the cylinder again 
with the gas, and lift it from the 
water in the same way, then turn it over and let it stand 
on the table open while I light a match. I bring the match 
to the mouth of the jar. 
Why is there no report ? 
Which is heavier, hydrogen or air ? 
What is the color of hydrogen? 

Ex. 19. — I put 30 cc. of water into the mortar, Fig. 6, and 
30 cc. strong hydrochloric acid. I drop into this a piece of 
zinc, and then place a small funnel, mouth down, over the 
zinc. I next bring the mouth of a test-tube 
down over the stem of the funnel, as shown 
in Fig. 15. The action should be brisk ; and 
if it be so, then, after one minute, I slowly 
lift the tube — keeping its bottom up — 
carry it away from the stem, and then bring 
a lighted match to its mouth. A dull explo- 
sion proves that the tube is full of hydrogen. 
The hydrogen rises through the air to the 
top of the tube, collects there and gradually 
pushes the air down and out at the bottom. If the explo- 
sion is sharp, it shows that the tube was only partly filled. 
Then repeat the experiment, and wait longer. 

Other gases which are lighter than air may be collected 
by this method, called upivard displacement. Oxygen, which 




Fig. 15. 




30 CHEMICAL CHANGES. 

is heavier than air, is collected (Fig. 5) by downward dis- 
placement. In Ex. 17 the gas was collected by displace- 
ment of water instead of air, and this method may be used, 
whether the gas is lighter or heavier than air. 

What causes the Explosion? Ex. 20. — I take a short 
piece of glass tube, which is drawn out to a small jet at one 
end, and fix it with a piece of rubber tubing 
upon the stem of the funnel. I again put 
dilute hydrochloric acid in the mortar, add 
the zinc, and place the funnel over it. The 
gas must come off very briskly ; and, if need 
be to make it do so, I add more strong acid. 
After about half a minute, if the gas is com- 
4ng fast, and longer if not, so that the air 
Fig. i6. shall be all driven out, I bring a match-flame 
to the top of the jet on the end of the funnel. The gas 
takes fire with the usual dull explosion, but goes on burn- 
ing as quietly as a candle. Eig. 16 shows this result. 
Then is hydrogen itself explosive ? 
Note also if the flame is pale or brilliant. 
Is it a hot flame ? Try it with a small wire. 
Ex. 21. — But what causes the explosion, if hydrogen 
can burn without it ? I will collect a little hydrogen 
over water, as in Ex. 17. But, instead of filling the cylin- 
der with the liquid, I will leave it about two-thirds full of 
air, filling only about one-third its height with the water. 
The liquid will soon be driven out, and then the cylinder 
is filled with a mixture of hydrogen and air. I now lift it 
from the pan, and at once bring a match-flame* below its 
mouth. A sharp explosion follows. 

What substances together explode in this case ? 
Have these same ones been together before whenever the 
explosion has occurred ? 

What, then, is the material which explodes ? 



CHEMICAL CHANGES. 



31 



What new Substance made by burning Hydrogen? 
Ex.- 22. — To answer this question I must burn pure dry 
hydrogen and catcli the products. I will make the hydro- 
gen as in Ex. 20, but before I light the jet I must dry the 
gas, and I can do this by passing it over calcium chloride, 
which absorbs water greedily. 

I take a "drying-tube," <x, Fig. 17, put a little cotton- 
wool in the bulb loosely, drop in small pieces of calcium 
chloride to fill the tube nearly full, and put a thin layer of 
cotton over it. I next close the large end with a cork hav- 
ing a hole, 1 through which I crowd the end of the stem of 
the funnel, b, Fig. 17. 

I now put several frag- 
ments of the zinc into the 
mortar ; afterward place 
the funnel over the zinc 
and fix the drying-tube 
firmly in the clamp of the 
support s, as shown in 
Fig. 17. This done, I 
pour dilute hydrochloric 
acid into the mortar. 

Hydrogen is set free. 
It goes up through the 
calcium chloride, which 
takes out the water. 
The dry hydrogen escapes from the jet above. 

After waiting until I am sure that the air is all driven 
out, I set fire to the dry hydrogen at the top of the tube, 
and then I hold a glass tumbler, or a wide-mouth bottle, 
which is clean and dry, over the flame, as shown at c. 

1 Holes are made through corks by means of " cork-borers/' made 
for the purpose. They may also be easily made by first running a hot 
pointed wire through the cork, and then using a round file to enlarge 
the hole. Each hole should be made to fit its tube very closely. 



Fig. 17 




32 CHEMICAL CHANGES. 

Notice a deposit of dew on the walls of the bottle; it is 
nothing but water. This is the substance made by burn- 
ing hydrogen in air. 

What are two other products ? See p. 28. 

Description of Hydrogen. — We have found that hy- 
drogen is a gas without color, and when pure it is also 
without odor and taste. It is very much lighter than air 
(Exs. 18 and 19). An equal bulk of air is 14.44 times 
heavier than this gas. In fact, hydrogen is the lightest 
of known substances. 1 

Hydrogen unmixed with air burns with a silent flame 
(Ex. 20), but when mixed with air the mixture burns with 
explosion (Ex. 21). The chemical action is the same in 
both cases : water, heat, and light are the products of this 
action (Ex. 22). There is nothing in this experiment to 
show what the hydrogen combines with to make the water. 
Let us remember this. 

The flame of burning hydrogen is very hot (Ex. 20). In 
fact, no other fuel gives so hot a fire as this. One gram of 
this gas will yield enough heat in burning to boil 344.62 g. 
of ice-cold water. 

A unit of heat is so much heat as will raise the tem- 
perature of 1 g. pure water 1° C. This unit is called a 
calorie, just as the unit of weight is called a gram. The 
heat of all chemical changes is measured by this unit. 
The burning of the gram of hydrogen gives 34462 of these 
units, or 34462 calories. 

Hydrogen gas is very seldom found in nature; it occurs 
sometimes among the vapors which are thrown out of vol- 
canoes. But the compounds of hydrogen are everywhere. 
Water is only one of them. Nearly all animal and vege- 
table bodies also contain hydrogen in large quantities. 

1 One liter of hydrogen weighs .0895 g. when its temperature is 
0° C., and the pressure of the air 15 lbs. per sq. inch. 



CHEMICAL CHANGES. 33 

Query. — A bottle stands mouth downward in water; it is full 
of gas ; how would you decide whether it contains air or oxygen 
or hydrogen? 

OXYGEN. 

Oxygen may be obtained by heating mercuric oxide, as 
in Ex. 5, or potassium chlorate, as in Ex. 6. The latter 
way is better, and a mixture of potassium chlorate with 
" black oxide " of manganese is still better than the chlorate 
alone. 

To make Oxygen. Ex. 28. — I take 4 g. of the chlo- 
rate and grind it to powder in the mortar. To this I add 
2 g. black oxide of manganese and mix the two powders. 
I put this mixture into the sicle-neck tube, Eig. 4, which I 
then cork tightly and fix in the clamp, as shown in the cut, 
Eig. 19. 

To catch and hold the gas, I use a set of flasks fitted up 
as shown in Eigs. 18 and 19. A conical flask 
is provided with a soft rubber stopper with 
two holes. A long glass tube passes through 
one of these holes in the stopper, and almost 
to the bottom of the flask ; a short glass tube 
passes only through the stopper in the other. 
I use four of these flasks, each holding about 
200 cc. 1 and a small bottle, e. Into the first one, a, I put 
sand enough to cover the bottom, and then some water, and 
I also put water into the bottle e. I then join them to- 
gether, as shown in Fig. 19, — the long tube of a with the 
side-neck of the ignition-tube, i, and the long tube of each 

1 This is a good size for the student's table. Larger ones may be 
used by the teacher for the class-room, and a flask may be used 
instead of the tube i for larger quantities. A set once fitted up is 
a sort of general gas-works for the laboratory, for, as we shall see, this 
method of collecting gas can be used for many other gases beside 
oxygen. 




34 



CHEMICAL CHANGES. 




of the others with the short tube of the one before it, 
the last rubber tube simply dipping into the water of the 
bottle. 

The gas will be "washed" by bubbling through the 
water in a, and then, too, one can tell by the bubbles in a 

and in e whether 
the gas is coining 
off fast or slow, 
and can regulate 
the heat accord- 
ingly. The use 
of the sand will 
be seen in Ex. 27. 
All the flasks 
must be closed air- 
^5T ..;<%£ tight; rubber stop- 
pers easily make 
air-tight joints. 
I now go on to make the gas. I make the flame of the 
Bunsen just high enough to not quite touch the ignition- 
tube, then lift the lamp and heat the mixture, gently at 
first, beginning at the part nearest the clamps, and mov- 
ing the flame to heat the tube uniformly. The decomposi- 
tion of the chlorate will gradually go on until it reaches the 
bottom of the tube. If the gas comes off too fast at any 
time I withdraw the heat for a moment. 

The gas will bubble through the water in a, and grad- 
ually fill that flask, pushing the air in it over into the next 
one, b. When a is full, oxygen will go over to the bottom 
of b, and will gradually fill that flask, pushing the air over 
into e. From c the air is driven over to d, and from d into 
e, the oxygen filling them all. One can be sure that the 
vessels are all filled with this gas by putting a lighted 
match into the mouth of e ; the flame will be brightened, 



Fig. 19. 



CHEMICAL CHANGES. 35 

When this test shows that the flasks are full of oxygen, 1 
or when all the chlorate is decomposed, if in any case too 
little is used, I withdraw the flame, and take off the rubber 
tubes from all the flasks. 

The Chemical Change. — Potassium chlorate is made 
of potassium, chlorine, and oxygen. It gives up its oxygen 
when heated, while the other two elements are left in the 
tube combined with each other. The manganese oxide is 
unchanged, and yet its presence is very useful, because it 
compels the chlorate to give up all its oxygen more stead- 
ily and with less heat. But just how it does this is not 
known. This is one of the cases in which a substance 
seems to act by its presence simply. A chemical action 
like this, that is, one due to the presence of a substance 
which remains unchanged, is called catalysis. 

To discover the Properties of Oxygen The flasks, 

used in Ex. 23 are full of oxygen. 

What is the color of this gas? 

The bottle e is also full : what is the odor of oxygen ? 

The bottle has now been standing some time open : is it 
still full of gas ? If so, then which is heavier, oxygen or 
air? 

Ex. 2Jf. — I remove the stopper from flask c7, hold the 
flask bottom up for two minutes, then stand it on the table 
and insert a lighted splinter of wood. 

Does the gas remain in the flask? 

Then which is heavier, oxygen or air ? 

Was this also shown by the bottle e? 

Oxygen and the Match. Ex. 25. — I wind a small 
copper wire (No. 20) around the white end of a burned 
match. I then heat the black end to a glow, and lower it 
a little way into the bottle e. The glow promptly becomes 

1 The amount of chlorate used (4 g.) will yield more than enough 
to fill these four flasks. 



36 



CHEMICAL CHANGES. 



a flame. I blow the flame out, and again lower the spark 
into the oxygen; the wood is promptly relighted. This may 
be repeated many times with the same flask full of gas. 

Oxygen and Carbon. Ex. 26. — I take a piece of char- 
coal — of the bark, if I can get it — and twist the end of a 
piece of fine copper wire around it for a handle. I then 
heat one corner of the charcoal until it glows and quickly 
lower it into flask c. After the burning is over I pour a 
little lime-water into the flask and shake it well. 

What effect has oxygen on the burning of charcoal? 
What effect is produced on lime-water afterwards ? 
What substance must be present to do this ? (See p. 17.) 
Oxygen and Iron. Ex. 27. — I take a piece of small 
iron wire (No. 23), and bind a piece of match to one end 
of it. I then set fire to the match and place it in the 

mouth of flask a, lowering it slowly 
as it burns away. The burning 
wood heats the iron until it too 
takes fire, and it then burns with 
surprising brightness. A slender 
watch spring would burn with still 
greater beauty. The sand catches 
the melted globules of iron as they 
fall, and may save the glass from 
being broken. 

Oxygen and Hydro- 
gen. Ex. 28. — Finally 
in the flask b I will burn 
a jet of hydrogen. I 
make the dry hydrogen 
as in Ex. 22. The only 
change in the apparatus 
is the addition of the tube r t, Fig. 20 ; r is rubber and t is 
glass, the lower end of which I held in the flame until the 




Fig. 20. 



CHEMICAL CHANGES. 37 

hole was nearly closed. Out of this small hole the gas 
comes in a small jet. After the air has been all driven out 
I set fire to the hydrogen and then plunge the small flame 
down into the oxygen in the flask, as shown in the cut. 

What change in the appearance of the flame ? 

What is the new substance on the walls of the flask ? 

What are the two constituents of this substance ? 

What must have combined with the hydrogen in Ex. 22 ? 

Where did the hydrogen there get it ? 

Description of Oxygen. — We have found that oxygen 
has neither color nor odor nor taste. It is about 1.1 times 
heavier than the same bulk of air. Oxygen combines read- 
ily with many things. It does so very rapidly when heated, 
and the chemical action yields both heat and light as well 
as new substances. A chemical action which yields both 
heat and light is called combustion. The heat and light of 
all common fires are due to the action of oxygen, which 
abounds in the air. 

Bodies which burn at all in air will burn with much 
more vigor in oxygen alone, as did the match and the char- 
coal in Exs. 25, 26. And many things which do not burn in 
air will burn freely in this gas, as did the iron in Ex. 27. 

When a thing is combined with oxygen it is said to be 
oxidized, and the new substance is called an oxide. Iron is 
oxidized when it burns in dry oxygen, and the new sub- 
stance made is the iron oxide. Carbon burned in oxygen 
(Ex. 26) is oxidized and carbon dioxide is produced, which 
will show its presence by whitening lime-water. 

But most substances must be heated before they will 
oxidize rapidly : neither wood nor coal nor iron will burn 
unless first made much hotter than they can ever become 
by exposure to the greatest summer heat. And yet the 
oxygen of the air is all the time acting upon many things. 
Wood decays and iron rusts ; these effects are due to 



38 CHEMICAL CHANGES. 

oxygen. But they are not produced quickly. Substances 
are oxidized, at ordinary temperatures, slowly. 

Oxygen in Nature. — About one fifth part of all the 
atmosphere is oxygen gas, and eight-ninths the weight of 
all the water of the earth consists of this element. In 
the bodies of animals and of plants oxygen is found in 
large proportions, and in the rocks immense quantities are 
combined. 

Query. — A bottle is full of a colorless gas ; how would you 
decide whether it is air or hydrogen or oxygen? 

Ozone. — Oxygen is very strangely changed by the action 
of electricity. If electric sparks are sent through oxygen, 
the gas will be found to have a very strong and peculiar 
smell, a little like that of burning sulphur. This strong- 
smelling oxygen will tarnish silver, which remains bright 
in oxygen that has not been electrified, and it will do much 
other chemical work which common oxygen cannot. Two 
cubic centimeters of it weighs as much as three cubic centi- 
meters of oxygen. In weight and odor and in chemical 
activity this electrified oxygen is as different from common 
oxygen as if it were another substance. 

And yet it can be nothing but oxygen. For the electric 
sparks cannot add anything to the pure oxygen they pass 
through, and so in going through it they cannot make a 
compound of the oxygen. And if the oxygen was decom- 
posed by the sparks, there would be at least another con- 
stituent set free beside this one; but there is not. 

We must confess that oxygen has two sets of properties ; 
the gas may exist in two distinct forms. The heavy, active, 
strong-smelling oxygen is called ozone. 

Just how the electricity changes oxygen to ozone is not 
known. But one thing is settled by experiment, and that 
is that the oxygen is condensed ; three volumes of oxygen 



CHEMICAL CHANGES. 39 

will make only two volumes of ozone. The electricity con- 
denses the oxygen in making ozone. 

Ozone is also made when acid-water is decomposed by 
electricity (Ex. 15). It is found in small quantities in the 
atmosphere, especially after thunder-showers, on account 
of the electric discharges, and its presence tends to purify 
the air; ozone oxidizes the impurities quickly and makes 
them harmless. 

Oxygen is not the only element 1 which can exist in two 
forms, as we shall see. This property of an element is 
called allotropism. Ozone is said to be an allotropic form 
of oxygen. 

EXERCISES IN CHEMICAL ACTION. 

1. Study the action of hydrochloric acid on sodium car- 
bonate by experiment. Proceed as follows : 

1. Bring the two substances together in a test-tube, and 
describe the action which takes place. 

2. Examine the gas which is given off to find out what 
it is. 

Note its color and its odor. 

Test it with a flame ; is it oxygen or hydrogen ? 

Is it heavier or lighter than air ? 
Collect a little of the gas in another test-tube. To do 
this, put a little of the carbonate into a side-neck tube, and 
put the rubber tube from this down into a test-tube. Make 
a very dilute acid by putting a cubic centimeter into the 
graduated cylinder and filling with water up to 25 cc. ; this 
dilute acid will not work quite so inconveniently fast as 
the strong. Now pour three or four cubic centimeters 
upon the carbonate, and cork the side-neck tube quickly. 
AVhen the action is nearly ended, add the acid again. Next 
pour a little lime-water into the test-tube with the gas and 
shake it well. 

1 See definition of element on p. 24. 



40 CHEMICAL CHANGES. 

What gas does it prove to be? 

3. Examine the liquid which remains in the side-neck 
tube to learn whether it contains any solid in solution. 
Filter it (Fig. 9), if it is not already perfectly clear. Then 
evaporate it (Fig. 10) until it is dry. 

Compare the solid found with the carbonate used. 
You can recognize this new substance by its taste. 

4. Write out a short statement of the facts which you 
have discovered about the action of hydrochloric acid on 
sodium carbonate. 

2. Study the action of hydrochloric acid on "Baking 
soda." Do this by experiments in just the same way as 
in Exercise 1. 

What are the two products of the action ? 
What, then, is " Baking soda " ? 

3. Study the action of dilute sulphuric acid on iron. 
Do this by bringing the acid in contact with some very 
small nails in a test-tube, closing the mouth of the tube, 
but not quite air-tight, with the finger. Then 

Find out whether the action is hastened by heat. 

If a gas is produced, test it, and name it. 

Find out by evaporation whether a solid is made also. 
And finally write out a short statement of all the facts 
which you have discovered about the action of dilute sul- 
phuric acid on iron. 

4. What is the difference between a physical change and 
a chemical change ? Between experiment and observa- 
tion ? Between analysis and synthesis ? What are ele- 
ments ? What are compounds? What are mixtures? 
What, besides new substances, may be produced by chemi- 
cal action ? What is combustion ? When is a substance 
said to be oxidized ? What is an oxide ? 



THE CHEMISTRY OF COMBUSTION. 



In ancient times only four elements were supposed to 
exist, and these were fire, air, earth, and water. It is now 
known that neither one of these is an element ; and as 
to fire, we know that it is not even a substance at all. Fire 
is the light and heat produced by chemical action. The 
chemical action which produces fire is called combustion. 

Between what elements is this chemical action taking 
place, and what new substances are made by it ? These 
are the questions we now set out to answer. 

Combustion of a Candle. Ex. 29. — I bring a clean and 
dry bottle down over the flame of a burning candle and 
hold it there for a little while, as shown in Fig. 21. 

What is the effect on the flame ? 

What gathers on the walls of the bottle ? 

Will lime-water be whitened if shaken in the bottle ? 

Thus we find water and carbon dioxide both made by the 
burning candle. But we know that it takes hydrogen and 
oxygen to form water (Ex. 28), and also 
that the air can furnish the oxygen 
(Ex. 22). So, when the candle burns, the 
air must furnish oxygen, and the can- 
dle must furnish hydrogen to form the 
water which it produces. 

In Ex. 26 we found that carbon diox- 
ide is made of carbon and oxygen. The 
carbon dioxide of the candle-flame must 
contain these same elements. The oxy- 
gen could come from the air ; the carbon must have come 
from the candle. Clearly the candle must contain carbon 
and hydrogen among its elements. And when it burns, 

41 




Pig. 21. 



42 CHEMISTRY OF COMBUSTION. 

the chemical action is between oxygen of the air and these 
elements of the candle. 

Combustion in other Cases. Ex. SO. — Burn a splin- 
ter of wood, a small roll of paper, a bit of cotton on a wire 
and moistened with alcohol, and a small jet of gas from 
the Bunsen lamp, in dry bottles, and see whether yon 
rind the same two products in each case. 

In the burning of a candle, of wood, of paper, of alcohol, 
of gas, — and in fact of all other common fuels, — the com- 
bustion is simply the combination of oxygen with the 
constituents of these substances. 

Carbon and hydrogen make up by far the larger part 
of all the substances which are used for fuel, and when the 
fuel burns carbon dioxide and water are always the chief 
products. When wood burns it is first decomposed by 
heat. Its carbon and hydrogen then take oxygen from the 
air and make carbon dioxide and water-vapor, and these 
two gases pass away in the smoke. 

Why did the flames all go out in the bottle ? 

The black part of smoke is the carbon which goes off 
without burning. 

A smoky flame is one that gets too little air. A lamp 
without a chimney smokes, but with a chimney the flame is 
clear and bright. It is so because the hot chimney makes 
a current of air sweep past the flame all the time, and this 
large quantity of air gives oxygen enough to burn the 
carbon completely. In every common fire much fuel is 
wasted as smoke, because the furnace is not built in a way 
to furnish air enough to burn up all the carbon. 

Combustion is a mutual chemical action, generally be- 
tween oxygen and some other substance, and which, when 
rapid enough, evolves heat and light. 

When a substance will burn in air, it is said to be com- 



CHEMISTRY OF COMBUSTION. 



43 



bustible: the air at the same time is said to be the sup- 
porter of combustion. But really there is no difference 
in the part played by the two things in the action : the 
chemical change is mutual. 

Heat a Product of Combustion. — Fuel is burned for 
the sake of the heat it can give, and not for the sake of 
the new compounds which it yields. The hottest kind 
of flame is that of hydrogen burning with oxygen. It is 
called the oxyhydvogen flame. 

Fig. 22 shows how this flame is obtained. The two gases 
are in separate bags, H and 0, or sometimes in iron cylin- 




Fig. 22. 



clers. They are pressed out of these through separate tubes 
into the "oxy hydrogen jet, ^ where they mix just before 
they reach the fire at the end of the jet. 

The two gases unite to form water, which goes away as 
vapor into the air. This chemical action is the source of a 
heat so intense that wires or strips of iron, steel, copper, 
zinc, and other things that do not burn at all in common 
fires, will burn in it almost as fast as a cotton thread will 
burn in a lamp-flame. 

If we burn hydrogen in air instead of in oxygen the heat 
is less intense because the chemical action is hindered by 
the large quantity of nitrogen which air contains. 



44 CHEMISTRY OF COMBUSTION. 

The quantity of heat will depend on the quantity of 
hydrogen which burns. Two grams of hydrogen will yield 
exactly twice as much heat as one gram, no matter whether 
it burns slowly or swiftly. But if it burn swiftly, more 
heat will be given in the same time, and the heat will be 
more intense. 

If a gram of hydrogen burns in the air instead of in 
oxygen it will still give the same quantity of heat, and 
yet the heat will not be as intense even if it burn in the 
same time, because some part will be used in heating up 
the large amount of nitrogen in air. 

We may say the same things of the heat when carbon 
or any other element is burned. The quantity of heat will 
always be the same for the same weight of the element 
burned, while the intensity of the heat will depend on the 
time it takes to burn it. 

But there is this difference, the gram of hydrogen will 
give more heat than the gram of carbon. There is just 
a certain amount of heat which the burning of a gram of 
each element will give, but this quantity is not the same 
for any two of them. 

Heat Required to Start Combustion A jet of gas, 

such as that from a chandelier, for example, escaping into 
the air, shows no signs of " taking fire," but touch it with 
a match-flame, and it instantly springs into vivid combus- 
tion. What has the match-flame done ? It has simply 
heated the gas. Illuminating-gas will not burn until it has 
a temperature of about 1000° F., and when the fire of the 
match has heated the jet up to this temperature it bursts 
into flame. 

The temperature at which a substance begins to burn in 
air is called its kindling-point. The kindling-point of most 
of our ordinary fuels is about 1000° F., but some other 
things begin to burn at a much lower temperature. Phos- 



CHEMISTRY OF COMBUSTION. 45 

phorus, for example, kindles at a temperature little higher 
than that of our ringers when we handle it. 

The kindling-point of a substance is the temperature at 
which it will begin to burn. 

In lighting a gas-jet the match-flame is needed only to 
heat the gas up to its kindling-point. 

All Flames are Gas Flames. — Let the wick of an alco- 
hol-lamp be uncovered ; no signs of flame are to be seen, 
but touch it with a lighted match, and very quickly an alco- 
hol flame appears. Now, the wick, to begin with, is wet 
with liquid alcohol. Then the heat of the match changes 
tins liquid into vapor, and afterward, quickly heats this 
vapor up to its kindling-point. When this double work is 
done the flame appears. 

The alcohol is in a gaseous form when it burns with a 
flame. 

We will suppose, next, that we have a candle which has 
been lighted and partly burned on some previous occasion. 
Its wick is saturated with cold and solid wax. We touch it 
with a match-flame. We notice that it takes more time to 
fire it than it does a spirit-lamp or. a gas-jet. The match 
has more work to do. It first melts the wax; it next 
changes it into vapor ; and then, finally, it heats the vapor 
up to its kincllingpoint. Not until this threefold work is 
done does the candle-flame appear. The wax is in the form 
of gas when it burns with flame. 

The wax of the candle, and the alcohol of the lamp, are 
changed into gases before any flame is seen, and this is 
true of other fuels also. Whatever burns with a flame must 
be at that moment in a gaseous state. 

Wood burns with flame, because it is first decomposed 
by the heat. Gases are formed, and the burning of these 
gases, and not of the solid wood, produces the flame. 

Hard-coal is made up almost entirely of solid carbon, 



46 CHEMISTRY OF COMBUSTION. 

which no furnace-heat can change into gas. As there are 
no gases first made by the heat, so there can be no flame 
produced in the burning. Hard-coal burns with a steady 
glow without flame. 

This is true if there is plenty of air for all the carbon, 
but sometimes there is not, and then carbon dioxide is 
formed, at first, as usual. But this afterward shares its 
oxygen with more carbon and becomes carbon monoxide. 
This carbon monoxide is a gas, and burns with a blue flame, 
which may be often seen playing over the surface of a hard- 
coal fire. 

Light a Product of Combustion — The very hot flame 
of hydrogen gives very little light, but if I hold a small 
iron wire in this flame the wire will quickly glow with 
light of a bright-red color. If a piece of lime is held in the 
oxyhydrogen flame it will shine with a dazzling brightness. 
The light made in this way is the well-known " lime light," 
also called the oxyhydrogen light. 

In both these cases the light is made by heating a solid 
substance which will not melt nor become a gas. Any 
flame which contains a solid substance which will not 
melt, nor become a vapor when heated, is a light-giving 
flame. Is there such a solid substance in a candle or a 
gas flame? 

Ex. 31. — I take a square of clean dry window-glass and 
hold it for a very short time across a candle-flame, just be- 
low the tip of it. I must remove it before it gets hot. 

What products are deposited on the glass? 

Ex. 32. — I close the holes in the tube of the Bunsen 
burner and the flame at once becomes bright. I next 
press a clean dry cold glass down upon it as I did upon 
the candle-flame before, and notice 

Whether the same products are left on it. 



CHEMISTRY OF COMBUSTION. 47 

Ex. 33. — Open the holes of the Bunseii burner and let 
the air enter. It mixes with the gas in the tube, and there 
is then oxygen enough among the particles of gas to satisfy 
both the hydrogen and the carbon at once. 

Compare the light with that when the holes are shut. 

The candle-flame and the gas-flame both leave a black 
coat upon the cold surface of the glass, and outside this 
spot a ring of dew may be seen. The black substance is 
carbon. The wax of the candle contains hydrogen and 
carbon. Now, when these two are offered to oxygen the 
oxygen will take hydrogen first. This is one fact. An- 
other is, that carbon is a solid which will not melt. 

We can now see how the light of a common flame is 
made. The burning substance is decomposed into hydro- 
gen and carbon. The oxygen of the air combines with the 
hydrogen first, and produces Avater, and great heat. This 
heats the particles of the carbon white-hot, so that they 
shine with a bright light. 

But the next moment this white-hot carbon unites with 
oxygen of the air, and is changed at once into invisible 
carbon dioxide. 

If the hydrogen and oxygen both burn at the same in- 
stant little light is given by the flame. The carbon changes 
to carbon dioxide as fast as the hydrogen does ; its par- 
ticles do not remain free long enough to shine. This is 
also the reason that the Bunsen flame is smokeless. The 
oxygen of air is mixed all through the gas and burns the 
carbon as fast as it is set free. 

But the heating of solid particles in a flame is not the 
only cause of the light. It has been found that some of 
the light comes from dense gases in the flame as well as 
from the solid particles. This explains why a lamp-flame 
is not so bright on the top of a high mountain as it is at the 
base. The gases in the flames are denser at the base, where 



48 



CHEMISTRY OF COMBUSTION. 



the atmosphere is heavier, than they are at the top of the 
mountain. 

A Common Flame is Hollow. Ex. 34. — I lay the 
stick of a common match right across a good candle-flame, 
just above the top of the wick, and leave it there only long 
enough for the flame to scorch it. Where it is not scorched 
of course there is no fire. 

Where is the fire, as shown by the stick? 

Ex. 35. — I take a square of paper and press it down 
upon the candle-flame almost to the top of the wick and 
take it away again just as soon as I begin to see the upper 
surface blacken, as shown in Fig. 23. 

Where is the fire, as shown by the charred paper ? 

Ex. 36. — The larger flame of an alcohol-lamp is better 
for the last two experiments than the candle. I plunge 

the head of a match in- 
to the dark center above 
the wick. The wood of 
the match burns in the 
edge of the flame, but 
the head of the match 
in the center does not. 

What is lacking, heat 
or air, or both ? 

In a candle or lamp 
flame the combustion goes on only around the outside, — 
in other words, the flame is hollow. There is no oxygen 
in the center of the candle or the gas flame. The dark 
space there is filled with the hot vapor of the wax or 
with gas, and the combustion goes on only where the air 
is in contact with the outside of this vapor. 

The burner of a chandelier is made so as to spread the 
illuminating-gas out into a fan-shaped sheet. This brings 




Fig. 23. 



CHEMISTRY OF COMBUSTION. 49 

a larger surface to the air and makes more light, but the 
chemical action is only on the outside of this thin sheet. 
The argand oil-burner does the same thing in another way. 
Its wick is thin and cylindrical, and air is made to pass up 
through the inside of it. The inside and outside together 
form a large surface. And then by using a chimney a 
draught is made by which more air than otherwise must 
pass up over the surface of the flame. The best light is 
produced by securing a full supply of air and a large 
surface to the flame. 

Queries. — What will be the effect of cooling a flame to a tem- 
perature below the kindling-point ? 

If a large piece of flat iron or stone is laid across a flame, as the 
paper was laid in Ex. 35, the flame will not touch it ; a thin space 
between them can be seen (try it). Why does the flame not touch 
the solid? 

Does a flame actually touch the bottom of a kettle in which 
water is being heated? Why? 

Why will a flame not pass through wire gauze ? But what if 
the gauze becomes red-hot ? 

Why does blowing a candle quench the flame ? Why does blow- 
ing a fire make it burn more briskly ? 



THE CHEMISTRY OF WATER. 

Analysis and Synthesis. — We have seen that there 
are two ways of finding the composition of a compound : 
one is called analysis, the other synthesis. In analysis we 
decompose the compound in such a way as to show what it 
is composed of, while in synthesis we combine the con- 
stituents in such a way as to show what they make. 

Experiment 28 was a synthesis of water, because we 




Fig. 24. 

brought hydrogen and oxygen together and found that 
they produced water when they combined. That experi- 
ment proved that water is composed of hydrogen and oxy- 
gen. But this is not enough. We wish to know whether 
it makes any difference if we use more or less of these ele- 
ments, and if it does, then we wish to know just how much 
of each is needed. Now that we know, by synthesis, what 
the elements of water are, we will try, by analysis, to find 

50 



CHEMISTRY OF WATER. 51 

out whether there is any particular quantity of each, and if 
so, then how much the water contains. 

Analysis of Water. Ex. 37. — How can we decompose 
water ? We have already found in Ex. 15 that electricity 
will set hydrogen free from acidulated water, and we will 
try electricity for our purpose now. 

Apparatus Needed. — We must have a battery, B, to 
furnish the electricity; two wires, w w, to carry the elec- 
tricity into the water ; two graduated cylinders, to catch 
the gases, the water-pan and the support. All these are 
shown in Fig. 24. 

The Battery. — Two cells of any good battery will de- 
compose water slowly, and a larger number more rapidly. 
If a battery is not at hand, one can be easily made as 
follows : * 

To make the Test-tube Battery. — Take 20 inches of 
round " carbon pencil, " used in small electric lamps. It 
should be about T 3 g-inch diameter, and cost a few cents. 
Saw this into five lengths of four inches each. 

Find five nails, each about the same length as the car- 
bons, and place them in a dish of dilute sulphuric acid. 
The acid will dissolve off the smooth, hard surface of new 
nails, so that they will act quickly when put into the bat- 
tery-fluid by and by. 

Get some flexible copper wire, — No. 18 is a good size to 
wind easily, — and finally also get the rack of test-tubes 
and a pair of pincers. 

Take a piece of the wire about four inches long, and 
wind one end of it around the end of a carbon rod twice, 
as tightly as it can be drawn, and then, lapping the short 
end over the wire, twist them with the pincers. This 
makes a close, firm joint. See Fig. 25, c. Then take one 

1 My test-tube battery is cheaply and easily made, and works vigor- 
ously. It is fairly constant for an hour and a half. It will yield 
hydrogen from acid-water at the rate of 1 cc. per minute. 



52 



CHEMISTRY OF WATER. 



of the nails, n, and wind the other end of the wire around 
it just below the head, drawing the wire as tightly as pos- 
sible. Roll the wire upon the nail until the carbon and 
nail are just far enough apart to let the couple hang close 
against the inside of two tubes when they stand in the rack, 
as shown at B, in Fig. 25 and Fig. 24. Make four of these 
couples and hang them in the tubes, so that there will be 
a carbon and a nail in each, except the first and the last. 
The carbons and nails must not touch one another. Then 
fix one carbon without a nail, and one nail without a car- 
bon, C, Fig. 25. Put the carbon in the tube with the lone 
nail, and the nail in that with the lone carbon, and put the 
ends of their wires into the small holes A, Fig. 24, made 
with an awl in the top of the rack. 

The Wires. — Cut two strips of platinum foil, each an 
inch long and a little less than half an inch wide, and two 
covered copper wires, say twenty 
inches long. Make one end of each 
wire very bright ; crowd it through 
a small hole near the end of a plati- 
num strip, bend it back on the other 
side, and press the loop carefully but 
tightly together to hold the platinum 
firmly. Now lay a thin piece of solder on the Avire where 
it touches the platinum, moisten it with a drop of hydro- 
chloric acid, and then hold it in the blue flame of the Bun- 
sen lamp until the solder melts, and no longer, lest the 
solder corrode and ruin the foil. In this way the wire and 
foil will be " soldered " together. 

The junctions of the platinum and wires, and so much of 
the wires themselves as will be in the water, must be well 
covered with parafflne. Melt some parafflne over a gentle 
heat, and before the liquid has become very hot put the 
lower end of the platinum and wire into it. 
See the foot-note on page 54. 





CHEMIST 11 Y OF WATER 53 

The Graduated Cylinders. — Use two of the gradu- 
ated cylinders shown at a, in Fig. 1. To support them : 
saw two slots in a pieee of thin board 
(Fig. 26, />), and then fasten it in the 
clamp of the support f, Fig. 5. The 
cylinders will hang bottom upward 
through these slots, as shown in 
Fig. 24. 

The Water. — Pure water will 
not let electricity go through it, but 
if it contains some sulphuric acid the electricity will go 
freely. Use about one-thirtieth as much strong acid as 
water, and fill the water-pan deep enough to cover the 
tops of the platinum strips half an inch when they stand 
upright, as shown in Fig. 26, a. 

The Battery Fluid. — Dissolve 35 g. of powdered po- 
tassium dichromate in 200 cc. of hot water. Then add 
24 cc. of strong sulphuric acid very slowly? all the time 
stirring the liquid. Use it when cold. 

The Expertmext. — Fill the cylinders by laying them 
in the pan of water, and then, lifting them bottom up, care- 
fully rest them in their support, as shown in Fig. 24. 

Not a bubble of air should remain in either one. 

Bend the wires to bring the platinum strips up under the 
mouths of the cylinders, and fix them in place by bending 
them tightly over the edge of the pan. See Fig. 26, a, and 
Fig. 24. 2 

1 Great heat is produced by adding the strong acid, and there is 
danger that drops of the hot liquid will fly out of the vessel. Let the 
acid run clown the side of the vessel in a very small stream while 
the red liquid is kept in motion. 

2 Or, better, the wires may be passed up behind the cylinders 
through small holes in the wooden support. The wires may be wedged 
tightly in these holes, and the platinum strips will then be held in 
place firmly while the wires are being handled during the experiment. 



54 CHEMISTRY OF WATER. 

Next, fill the test-tubes nearly full of the battery fluid, 
put globules of mercury into the holes h, and finally put 
the ends of the wires from the water-pan into these holes, 
noting by the watch the time when the last is inserted. 

Bubbles of gas instantly form on the platinums, break 
away, and rise into the cylinders ; see that none escape 
outside. 

Note the number of cubic centimeters of gas in each 
cylinder : 

At the end of 2 minutes. 

At the end of 5 minutes. 

At the end of 10 minutes. 

Do you find the larger quantity over the platinum which 
is joined to the carbon or to the iron of the battery ? 

Which is Hydrogen and which is Oxygen ? Ex. 88. — 

I test the gases with a match-name. Holding a lighted 
match in my right hand, I grasp the cylinder which is 
over the plantinum of the wire which comes from the iron 
of the battery, and, closing its mouth as well as I can 
with my thumb, I lift it out of the water, turn it quickly 
mouth upward, and at the same time bring the flame to 
its mouth. The gas burns with explosion. 

I next test the gas in the other cylinder in the same way ; 
the match burns with unusual brilliancy, or a long splinter 
of wood with a spark of fire thrust down into the gas 
bursts into flame. 

What are the relative volumes of hydrogen and oxygen ? 

The Pacts The current of electricity decomposes the 

acid water. Hydrogen and oxygen are the only substances 
produced. And there are always twice as many cubic cen- 
timeters of hydrogen as of oxygen. 1 

1 Oxygen combines with copper, and if the wires and solder are not 
completely covered with paraffine where they touch the liquid, some of 
the oxygen will be used up in this way. 



CHEMISTRY OF WATER. 55 

These facts mean that water is made up of two measures 
of hydrogen and one measure of oxygen. 

A Source of Doubt. — But the water was not pure, and 
some part of these gases may have come from the acid in it, 
or have been used up by it. So this analysis alone does not 
prove the composition of water beyond doubt. In fact, it is 
only one source of evidence, while there are many others. 1 
We may mention one. By measuring the hydrogen and 
oxygen gases, and then passing an electric spark through 
the mixture, they are made to combine, and in every case 
it is found that just twice as many cubic centimeters of 
hydrogen as of oxygen have been used to produce water. 

All the facts when taken together prove that pure water 
is composed of 

Two volumes of hydrogen and one volume of oxygen. 

Composition by Weight. — But hydrogen is much 
lighter than oxygen. In fact, it is found that one measure 
of oxygen weighs eight times as much as the two measures 
of hydrogen. So that by iv eight, pure water is composed of 

One part of hydrogen and eight parts of oxygen. 

One ninth part of any weight of water is hydrogen, and 
the other eight ninths of it is oxygen. 

Then how much of each must there be in 100 grams ? 
One ninth of a hundred, or 11.11 of hydrogen, and eight 
ninths of a hundred, or 88.89 of oxygen. The chemist 
writes this composition of water thus: 

Hydrogen ...... 11.11 

Oxygen 88.89 

Water ........ 100.00 

And this is called the percentage composition of water. 
Composition by Volume. — We have just seen that 
water when it is decomposed yields just twice as many 
1 See Roscoe and Schorlemmer, pp. 204, 212. 



56 CHEMISTRY OF WATER. 

cubic centimeters of hydrogen as of oxygen. When we 
had 20 cc. of hydrogen we had also just 10 cc. of oxygen. 
But we did not notice how much water gave us the 20 cc. 
of one and the 10 cc. of the other. The fact is that it 
takes only about ^ part of 1 cc. of the liquid, and this is 
so small a quantity that we do not see the loss of it in 
the experiment. 

But while 20 cc. of hydrogen and 10 cc, of oxygen will 
make so little of the liquid water, they will of course make 
a great deal larger volume of water vapor. It has been 
found that they will make just 20 cc. The volume of the 
water, in vapor, is just the same as the volume of the 
hydrogen alone. The fact is that 

Two measures of hydrogen and one measure of oxygen 
make two measures of water-vapor. Or three volumes of 
the constituents are condensed to two volumes of the com- 
pound. 

Make a note of this curious fact. 

The Constant Composition of Water. — Water has 
been analyzed over and over again with the same result. 
The synthesis of water also has been repeated a great many 
times, and the same proportions of the same elements have 
always been found. It is, therefore, quite certain that pure 
water is always made up of the same elements and in the 
same proportions by volume and by weight. 

The Constant Composition of other Compounds.— 
We may mention hydrochloric acid. It has been proved 
by both analysis and synthesis that this acid is always 
made up of hydrogen and chlorine, in the proportions' of 
1 part by weight of hydrogen to 35.5 parts of chlorine. 
Its composition is as constant as that of water. 

And common salt, from whatever source it comes, always 
contains the same two elements, — chlorine and sodium, 
and always in the proportions of 35.5 parts of chlorine to 
23 of sodium. 



CHEMISTRY OF WATER. 57 

The Law of Constant Proportions. — So many com- 
pounds have, like these just named, been found to have a 
constant composition, that the chemist is cpiite sure that 
all compounds are alike in this respect, and he states this 
conclusion as follows : 

Any compound is always made of the same constituents 
and in the same invariable proportions. 

This important statement of fact is known as the law of 
constant proportions. 

Water in Nature. — Hydrogen and oxygen are the only 
constituents of all pure water. Bat pure water 
is not to be found in nature. Even the rain- 
drop, which has never touched anything but the 
air through which it falls, is not pure, and it is 
still more impure after it has touched the earth. 
Why is water always impure ? And what are 
its impurities ? These are the questions which 
we Avill try next to answer. lg " 

Ex. 39. — I fill a bottle three-fourths full of clear water. 
I cover it with a piece of muslin loosely, and bind the cover 
in place by a string around the neck. I put half a tea- 
spoonful of powdered cochineal on the cover, and then pour 
some clear water slowly upon it. The water very soon 
trickles through the cover and falls into the water below. 
But instead of being clear and colorless, it falls from the 
cover in a crimson stream. Why ? 

Ex. Jfi. — I repeat Ex. 39, but in place of the cochineal 
I use some powdered copper sulphate. The stream which 
falls into the water is Hue. Why ? 

Ex. Jf.1. — I prepare a flask of hydrochloric acid gas in 
this way : I put 40 or 50 cc. of strong hydrochloric acid into 
a side-neck flask, /, Fig. 28, and fix the flask in the clamp of 
the support. I join the side-neck to the long tube of the 




58 



CHEMISTRY OF WATER. 




flask <7, and the short tube of a with the long tube of b. 
And now, all the joints being tight, I gently heat the acid. 

Hydrochloric acid gas will 
go over, driving the air be- 
fore it, until the flasks are 
full. When the gas issues 
freely from b it will make 
itself known ; then I with- 
draw the flame, and at once 
take both rubber tubes from 
I then take the stopper 
from the flask, and at the 
same time cover its mouth 
^g- 28 - with the palm of my hand. 

I now turn the flask bottom upward and lower its mouth 
into the water of the pan, as shown in Fig. 29. The water 
rises — it should rise quickly — into the flask. Why ? 

Cochineal readily mixes with water, and gives it a crim- 
son color. And yet not a particle of 
cochineal can be seen in the crimson 
liquid. It is divided into pieces too 
small to be seen, and these pieces are 
uniformly scattered, giving color to 
every part. The cochineal was cits- Fig - 29 - 

solved by the water. The red liquid (Ex. 39) is a solution 
of cochineal in water. 

AVater also dissolves copper sulphate (Ex. 40), and the 
solution is blue. 

Salt is also soluble in water ; but its solution, brine, is 
without color. A vast number of other solids are more or 
less soluble in water. Some of them give it color ; others 
give no visible sign of their presence. The most colorless 
water may hold many and a great deal of these soluble 
bodies. They are its impurities. And all water that has 




CHEMISTRY OF WATER. 59 

been in contact with soil and rock holds more or less of 
these impurities. 

Gases also are soluble in water. Hydrochloric acid gas 
dissolves in large quantity (Ex. 41) ; 100 cc. of water will 
take up 45,000 cc. of this gas at a temperature of 15° C, — 
more if it be colder and less if it be warmer. Hydrogen is 
slightly soluble in water, oxygen a little more so ; 100 cc. 
of water will take only about 3 cc. of oxygen. Water ab- 
sorbs the gases of the atmosphere. These also are impuri- 
ties in all natural water. 

Mineral Waters. — When water holds enough of any 
one thing in solution to give it a peculiar taste it is called 
mineral water. Such a water receives the name of the 
substance in it, and so does the spring from which the 
water issues. Sometimes a spring yields water in which 
compounds of iron are dissolved ; it is then called an iron 
spring, or a chalybeate spring. Sometimes the compounds 
of sulphur are present in large quantity ; the water is then 
a sulphur-water. 

When water holds much lime or magnesia compounds in 
solution it is called hard water ; when nearly free from 
these it is called soft ivater. 

Drinking- Water. — Good water for household use always 
contains air in solution. On standing quietly in a warm 
place a vessel of water will show bubbles of air clinging to 
the inside surface. Try it. This air if pure is not only 
wholesome but helps to make the water palatable. But 
water will absorb bad gases as freely as the good; drinking- 
water should not be allowed to stand in bad air. 

Water which holds a small quantity of mineral matter in 
solution is also wholesome, but never when it contains ani- 
mal substances. Typhoid fever, diphtheria, and some other 
diseases, are frequent where the water used in households 
is charged with even very small quantities of animal sub- 
stances. 



60 



CHEMISTRY OF WATER. 



Vegetable matter is less dangerous than animal matter, 
but when much is present it likewise makes the water unfit 
for household purposes. 

Water which holds fine particles, whose impurities are 
in the form of sediment, may be purified by filtration. On 
a large scale, the water for cities is filtered through beds 
of sand and gravel. 

But the most deadly impurities of water are often in 
solution, and these no such filter can take out. Charcoal- 
filters may remove small portions, but they cannot be 
trusted to purify bad waters for household use. 

Distillation. — Pure water can be obtained by boiling 
common water and catching the steam in a cold vessel. 
This process is called distillation. 

Ex. J$. — I place 50 cc. of water in my side-neck flask 
and close it with a cork through 
which I have pushed the stem of a 
thermometer, as shown in Fig. 30. 
To the side-neck I join a long glass 
tube by slipping a short piece of 
rubber tube over the end of each. 
I put the end of 
the glass tube 
down into a test- 
tube, which I lay 
in the water-pan 
nearly filled with 
cold water, and 
finally I heat the flask with a Bunsen lamp. 

Note every effect you can see while the water is being 
heated. 

Keep watch of the mercury in the thermometer before 
the water boils. 




Fig. 30. 



CHEMISTRY OF WATER. 



61 



Keep watch of the mercury in the thermometer after the 
water boils. Note the temperature. 
What happens in the test-tube ? 
The Facts. — Long before water boils bubbles may be 

seen escaping from it ; these are bubbles of air which was 
in solution. Afterward the water boils and the steam goes 
over into the test-tube, where it is at once changed back 
into water by cold. But it is only the water which goes 
over as steam ; the solid impurities stay in solution in the 
flask because they need so much more heat than water does 




Fig. 31. 

to change them into vapor. The water in the tube is nearly 
pure ; it is called " distilled water." And this way to 
purify a liquid is called distillation. 

The thermometer shows that in this process the water 
becomes hotter and hotter until it boils, but not afterward. 
When the thermometer marks 100° C. it goes no higher, 
though the water boil never so hard. This temperature is 
called the boiling-point of water. On a Fahrenheit ther- 



62 



CHEMISTRY OF WATER. 



mometer this point is marked 212°. Other liquids also are 
purified by distillation. 

Fig. 31 shows a complete apparatus, used by chemists, 
for the distillation of liquids. The liquid is boiled in the 
flask. Its vapor goes through the inside tube of the con- 
denser c, while the larger tube outside it is kept full of 
cold water. Here the vapor is changed back to liquid 




Fig. 32. 



and this liquid drops into the receiver B. Kubber tubes 
carry the cold water to and from the condenser c. A ther- 
mometer, t, may be used to show the boiling-point of the 
liquid. 

Effects of Cold. — A given weight of water, say 10 g., 
will grow smaller and smaller as we make it colder. Its 



CHEMISTRY OF WATER. 63 

volume will be less and less until its temperature is 4° C. 
But if we cool it below this point the water will expand. 
Its volume will then become greater and greater quite 
regularly until it is cooled down to 0° C. At 0° the water 
suddenly expands much more, and at the same time it 
begins to freeze. This temperature at which water freezes 
is called the freezing-point of water. It is 0° C. or 32° F. 

Ice is crystallized water. In blocks of ice the crystals 
are so crowded together that their forms are lost. The 
shapes of ice-crystals are seen in the beautiful frost-figures 
on the window-pane in winter and in snow-flakes, some of 
whose curious forms are shown in Fig. 32. 

EXERCISES. 

1. Study the effect of mixing snow and salt. 

Take snow or pounded ice, add salt gradually, stirring 
the two well together. 

What change takes place in the two solids ? 
Get the temperature of the mixture. 

2. Compare the freezing and melting points of water. 

1. Put a small bottle or a test-tube partly filled with 
water into the freezing mixture just made, and stir this 
water with the bulb of a thermometer carefully until it 
begins to freeze. 

At what temperature does the freezing begin ? 
Does the temperature change afterwards ? 

2. Fill a wide-mouth bottle with small pieces of ice and 
let it stand. Afterward stir the ice about in the water 
and take the temperature of the mixture. 

At what temperature does the ice melt ? 
Eepeat these two experiments and decide whether they 
show that there is, or is not, a difference between the 
melting-point of ice and the freezing-point of water. 



64 CHEMISTRY OF WATER. 

3. Find the boiling-point of alcohol, Fig. 30. 

4. Find the boiling-point of a mixture of alcohol and water 

made in the proportion of one volume of alcohol to 
two volumes of water. 

Use the apparatus shown in Fig. 30. 

Note the temperature when the boiling begins. 

Turn the lamp low and let the boiling go on slowly 
until about 5 cc. of distillate is caught. Then change the 
test-tube. 

Note the boiling-point again. 

Eepeat this several times, and then compare the distil- 
lates, by their odors and by means of a match-flame. 

Which contains the most alcohol ? 

Does the liquid in the flask still contain alcohol ? 

The fact is that two liquids which have not the same 
boiling-point can be roughly separated by this process of 
distillation. It is called fractional distillation. 

5. Find by evaporation, whether the tvater in use holds any 

solid matter in solution. 
How, by the use of the balance and the graduated cylin- 
der, can you find how much of this mineral substance the 
water contains ? 



CHEMISTRY OF THE ATMOSPHERE. 

Not one hundred years ago the air was thought to be an 
element ; that it is not was proved by the great French 
chemist Lavoisier. 

Lavoisier's Experiment. — The apparatus which he used 
was much like that shown in Fig. 33. A small quantity of 
pure mercury was put into a flask which was placed over 
a furnace. The flask had a long, slender neck, which 




Fig. 33. 

reached over into a pan of mercury. Standing mouth 
downward in this pan was a jar filled with air, and the 
neck of the flask was bent up into it. 

When all was ready, Lavoisier lighted the fire in the 
furnace and kept it burning all the time for twelve days. 
On the second day he saw little red flakes of something 
swimming around on the surface of the mercury. For four 
or five days afterward the quantity of this reel substance 

65 



66 CHEMISTRY OF THE ATMOSPHERE. 

increased while the quantity of air in the receiver dimin- 
ished. For some time longer the heat was kept up, but no 
further change took place, and this part of the work was 
done. He had less air in the apparatus than at first, shown 
by the mercury rising in the jar, but instead of the air 
which was lost he had the new red substance in the flask. 

What was this red substance ? To find out, Lavoisier 
heated it in a tube so fixed that any gas which should be 
produced would be caught in a vessel over mercury. The 
red substance became black, then began to waste away 
while bubbles of a colorless gas were caught in the vessel 
prepared for the purpose, and globules of shining mercury 
gathered on the walls of the tube above the heated part. 
What was the colorless gas ? Lavoisier plunged a candle- 
flame into it ; the candle burned with a dazzling light. 
The gas was oxygen. 

But whence came this oxygen to combine with the mer- 
cury when it was heated with air in Lavoisier's flask ? The 
air must have given it to the mercury, and so the experi- 
ment proved that oxygen is one constituent of air. 

In the flask and the glass jar (Fig. 33) there was still left 
a large quantity of air-like substance. But on plunging a 
candle-flame into it the flame was put out as it would have 
been in water. Plainly it was not air. In fact it was the 
gas called nitrogen. 

Lavoisier's experiment proved that oxygen and nitrogen 
are two constituents of air. There are indeed a few other 
gases in the atmosphere beside these, but in comparison 
with these the quantity of them is small. Oxygen and 
nitrogen are the two chief constituents of the air. 

NITROGEN. 

When a substance burns in air it takes the oxygen and 
leaves the nitrogen. Lavoisier burned mercury, but sul- 




CHEMISTRY OF THE ATMOSPHERE. 67 

phur and some other things will burn more quickly, and 
may be used instead. Let us try sulphur, and afterward 
phosphorus. 

Ex. 43. — I cut a slice half an inch thick from a cork 
which is much smaller than the 
mouth of my bottle. I shape the 
top of the cork into a shallow cup 
and rub it well with crayon-powder, 
or better with a paste of moistened 
plaster of Paris. I put sulphur in Jjj 
this cup, place the cup on the shal- 
low water in the water-pan, set fire Fls " 34 ' 
to the sulphur, and put a bottle bottom upward over it, as 
shown in Fig. 34. Describe 

The flame of the sulphur. 

The action of the water when the burning is over. 

The change in the gas after long time standing. 

Ex. 44- — I use a piece of phosphorus, not larger than a 
good-sized kernel of wheat, with another bottle holding 
about 200 cc. I treat it just as I did the sulphur, and 
again describe the flame, the action of the water afterward, 
and the appearance of the gas inside after standing some 
time over water. 

But the handling of phosphorus is dangerous, unless it 
is done with great care. Phosphorus takes fire easily and 
burns the flesh cruelly. Cut it under water, lift the piece 
with the knife-blade, dry it by gentle contact with filter- 
paper, and put it into a dry cup. Never handle phosphorus 
without using the greatest care. 

Ex. 45- — When the gas in the bottle used in Ex. 43 has 
become clear I slip a square of glass or of cardboard under 
the mouth of the bottle, lift it out of the water, turn it 
mouth upward, stand it on the table and leave it covered, 



68 CHEMISTRY OF THE ATMOSPHERE. 

I at once ignite a match, uncover the bottle, and insert 
the flame; the nitrogen will quench it. I leave the bottle 
uncovered. I treat the bottle used in Ex. 44 in the same 
way ; the nitrogen again puts out the flame. I leave this 
bottle, also, uncovered. 

Ex. Jfi. — I now again insert a match-flame in the bottle 
first left uncovered, and afterward in the other. The flame 
is not quenched. 

What does this prove? 

Ex. Jj.7. — I now add a little blue litmus-water to the 
water in the bottle in which sulphur was burned. 

Note the change of color. Compare Ex. 8. 

What causes this change of color ? 

Ex. £8. — I add blue litmus-water to the water in the 
second bottle which was left uncovered in Ex. 45; it 
changes from blue to red. 

Can you explain this change of color ? 

Burning of Sulphur Sulphur, when burning with its 

feeble blue flame, combines with oxygen, and the two 
become sulphur dioxide. The water soon dissolves the 
whitish vapor and rises into the vessel, and at last fills 
just the space which the oxygen of the air occupied at 
first, while the nitrogen of the same air remains above the 
water (Ex. 43). 

The sulphur dioxide shows its presence in the water by 
reddening the blue litmus, Ex. 47, as it did in Ex. 8. 

Burning of Phosphorus. — When phosphorus is used 
the action is much the same. It combines with the oxy- 
gen of the air and forms phosphoric oxide, which fills the 
vessel as a milk-white vapor. Water soon dissolves this 
oxide, and the nitrogen of tire air is left as before. 

The phosphoric oxide also shows its presence in the water 
by reddening blue litmus (Ex. 48). 



CHEMISTRY OF THE ATMOSPHERE. 69 

Properties of Nitrogen. — Nitrogen is a colorless gas 
(Exs. 43, 44). It is lighter than air (Ex. 46), but a liter of 
it weighs fourteen times as much as a liter of hydrogen. 
It will quench fire (Ex. 45), because it cannot unite with 
the elements of the fuel as oxygen does. In fact, nitro- 
gen is the least active of the elements. It will not only 
quench fire, but if breathed instead of air it will quench 
life also. Yet it cannot be poisonous, since we inhale it 
with every breath without injury. It is the oxygen of the 
air that sustains life, and it is the absence of oxygen, and 
not the presence of nitrogen, which causes death when pure 
nitrogen is breathed. 

Other Constituents of Air. — The air also contains 
water in form of invisible vapor. This is proved by placing 
a piece of caustic potash in an open dish. The potash 
will very soon become wet, and if left for some time it 
will be dissolved by the water which it takes from the air. 
Try it. The moisture to be seen on the outside of a vessel 
of ice-water in summer is the condensed water-vapor of the 
air. Dew and hoar-frost are also the water of the air, 
changed by cold from vapor to liquid and solid forms. 

The air also contains carbon dioxide. This is shown by 
lime-water, which if left exposed in an open vessel will 
become covered in a few hours with a white crust. Try it. 
This crust is the same substance which is seen in lime- 
water after it has received carbon dioxide (Ex. 7). 

The air also contains ammonia in very small quantities. 

Nitrogen, oxygen, water-vapor, carbon dioxide, and am- 
monia are the regular constituents of the atmosphere. Our 
next question is, How much of each of these substances is 
to be found in air ? 

The Analysis of Air. — We set out now to find how 
many cubic centimeters of nitrogen and how many of oxy- 
gen and carbon dioxide there are in 100 cc. of air. 



70 



CHEMISTRY OF THE ATMOSPHERE. 



To do this we will imprison a vesselful of air, and then 
run into it a liquid which will absorb both the oxygen and 
the carbon dioxide completely, and leave the nitrogen. We 
can then measure the nitrogen which is left, and we can 
find out how much there was of the other two, by measur- 
ing the liquid which has gone into the tube to take their 
place. 

Ex. 49. — Our Apparatus. — I take a test-tube, t (Fig. 
35) to hold the air. A six-inch tube, f inch in 
diameter, will do ; an eight-inch tube of the same 
diameter is better. The rubber stopper, c, is so 
large that its small end will enter the tube only 
about a half -inch. It has two holes ; to close 
one I have a solid rod of glass, s ; for the other, 
a glass tube reaching just a very little below the 
cork, as shown. A piece of thin rubber tubing, 
h, is cut about six inches long. There is a pinch- 
cock, p, by which its walls may be pinched so as 
Fig. 35. ^ c i ose jt completely. F is a small glass funnel. 
The lower end of h I stretch over 
the tube in the cork e, and its upper 
end I fix over the stem of F, and then 
I place the funnel in the clamp of the 
support, as shown in Fig. 36, and re- 
move the rod s. 

The Liquid. — To absorb the oxy- 
gen and carbon dioxide gases I use 
a mixture of pyrogallic acid and po- 
tassium hydrate. 

I take a small teaspoonful of the 
solid acid and pour on it 10 cc. of 
water ; it will soon dissolve. To this 
I then add 5 cc. of strong solution of potassium hydrate, 
and at once pour it into the funnel. ISText, I hold the dish 





Fig. 36 






CHEMISTRY OF THE ATMOSPHERE 



71 




Fig. 37. 



below the cork and open the pinch-cock p a moment, to 

let the liquid run down and fill the tnbes completely. I 

carefully take off the drop, which hangs 

at the lower end of the tube below the 

cork, with a piece of filter-paper. 

I press the tube t up over the cork 

until the joint is air-tight, as seen in 

Fig. 37, and after a minute I put the 

rod s into the open hole of the cork. 

I have now imprisoned a tubef ul of air ; 

none can get out, and no more can 

get in. 

I left the hole in the cork open, be- 
cause if it were not open the pressure 

of the cork would ciwvd the air below, 

and there would be too much in the 

tube; and then, too, handling the tube warmed it, and the 
volume of air changes with heat. 
With the hole open, the air in the 
tube soon comes to be just as warm 
and just as much pressed as the air 
outside. Whenever a gas of any kind 
is to be measured its temperature and 
pressure must be the same as those of 
the air outside. 

The Absokptiox. — I now press 
the pinch-cock p; a little stream of 
the liquid falls into t at once, and 
then drops follow, or, if the tube be 
slightly inclined, a slender stream will 
flow down its side. It will continue 
Fig- ss. to enter as long as there is any oxy- 

gen or carbon dioxide for it to absorb, and then stop. 
The gas which is left in the tube is nitrogen. 




72 CHEMISTRY OF THE ATMOSPHERE. 

But this gas is crowded down by the pressure of the 
liquid in the rubber tube and funnel above, and so I take 
hold of the cork c, and the rim of t, not to warm the gas 
with my hand, and lift the tube bottom up, as shown at 
T in Fig. 38, making the level of the liquid the same in 
the tube and in the funnel. I then open the pinch-cock. 
Some of the liquid will run out of T. When the liquid 
stands at the same level in the tube and in the funnel, I 
close the cock and bring the tube down again. 

The almost black liquid in t has now taken out all the 
oxygen and carbon dioxide from the tubeful of air, and 
left all its nitrogen. 

The Measuring. — I must measure the liquid in the 
tube to find how much oxygen was taken out, 1 and the 
space above it to find how much nitrogen was left. 

To do this I slip two small rubber rings up on the tube, 
and make the upper edge of one mark the place of the 
lower end of the cork, and of the other, the top of the 
liquid. These rings must not afterward be disturbed. 

I may now remove the cork, empty the tube, rinse it 
with water, and then let the last drop of water drain away. 
Finally, I use my graduated cylinder to find out exactly 

How many cc. water will fill the tube to the first ring. 

How many cc. water will fill the tube from the first to 
the second ring. 

The Calculations. — From these two numbers we can 
find what part of the air is nitrogen and what part is 
oxygen. For they help us to answer the following 
questions, in their order, one after another, as shown 
by an example below. 

1 And carbon dioxide also. But the volume of the carbon dioxide, 
in so small a quantity of air as we use, is so little that we cannot 
measure it with our apparatus. We may leave it out of account in 
this experiment. 



CHEMISTRY OF THE ATMOSPHERE. 73 

How many cc. of air were in the tube at first ? 
How many cc. of nitrogen did this air yield ? 
How many cc. of oxygen did the same air yield ? 
Then what fractional part of the air is nitrogen? 
What fractional part of the air is oxygen ? 
And how many cc. nitrogen in 100 cc. of air ? 
How many cc. of oxygen in 100 cc. of air ? 

An Example. — In an actual experiment it was found 
to take of 

Water to fill the tube to the first ring ..... 6.0 cc. 
Water to fill the tube from the first to second ring . 23.5 cc. 

Hence the number of cc. of air taken 29.5 cc. 

And the number of cc. of nitrogen found . . . . 23.5 cc. 
And the number of cc. of oxygen found .... 6.0 cc. 

Now this would show plainly that fff of the air is nitro- 
gen and 2 6 9°5 of it is oxygen. Then in 100 cc. of air there 
would be 

Nitrogen 79.66 cc. 

Oxygen 20.34 cc. 

The Exact Composition of Air. — Some of the great- 
est chemists have devoted much time to find out exactly 
how much oxygen and nitrogen the air contains. They 
have used other methods, more accurate than that of ab- 
sorption, and apparatus much more refined than that which 
has answered our purpose. 1 They have found the per- 
centage composition to be 

Nitrogen 79.04 

Oxygen -. 20.96 

Air 100.00 

1 For full description, see Roscoe and Schorlernmer, Vol. I. pp. 
439-447. 



74 CHEMISTRY OF THE ATMOSPHERE. 

When the gases are weighed instead of being measured 
the numbers are different. Tims : 

Nitrogen 77.00 

Oxygen 23.00 

Air 100.00 

How much Water-vapor in Air? — The quantity of 
water-vapor in the air is all the time changing. There is 
only a certain amount which air can hold at any given 
temperature, and the only way to make it able to take 
any more is to heat it. 

But the atmosphere seldom has all that it can hold. 
At 60° F. the quantity will be usually found between ^ 
and ^q of the bulk of the air. 

What Fraction of the Air is Carbon dioxide ? — 
Sometimes as much as joV o °f the air ^ s carbon dioxide ; at 
other times or places there may be no more than ^oW 
Perhaps the average proportion may be osVo- 

So small a quantity as one cubic inch of this gas in 
twenty-five hundred cubic inches of air seems, at first 
thought, too small to be worthy of notice. It is not so. 
Carbon dioxide, little as there is of it, is one of the most 
important substances in the atmosphere. Plants cannot 
grow without it. It is a needful part of their food, and 
they are, when growing, all the time taking it out of the 
atmosphere. It is returned to the air by the breathing of 
animals, by the burning of fuels, by the decay of plants, 
and by volcano s. 

We will shortly make a special study of this gas, but for 
the present we go on with the description of air. 

The Atmosphere a Mixture or a Compound ? — It is 
found that the carbon dioxide of the air makes lime- 
water turbid just as the same gas from marble will do. The 
water-vapor in the air may be condensed to liquid by cold, 



CHEMISTRY OF THE ATMOSPHERE. 75 

just as water-vapor alone may be. Bodies burn in oxygen ; 
they burn also in air, of which oxygen is a constituent= 
Xitrogen alone extinguishes fire completely, and nitrogen 
in the air strives to do so, but succeeds only in making 
them burn more feebly in the oxygen which is present. 
In fact, the properties of the constituents of air can be 
easily detected in the atmosphere itself. 

But when substances combine they form a compound in 
which their own properties are not" to be found. We 
therefore say that the atmosphere is not a compound, but 
a mixture. 

Constant and Uniform in Composition The pro- 
portions of oxygen, nitrogen, and carbon dioxide are always 
very nearly the same. Air on the tops of mountains, and 
in the low places of the earth, and in different countries, 
have all these constituents, and very nearly the same rela- 
tive quantities of them. 

The heavy carbon dioxide, the lighter oxygen, and the 
still lighter nitrogen, are uniformly mixed together. Why 
do they not separate into layers, as water and oil would do 
after having been mixed never so perfectly ? 

Diffusion of Gases. — The fact is that gases will not 
stay unmixed if they touch each other. We 
may bring a light gas on top of a heavy one, 
and find that a part of the light one will 
sink, and a part of the heavy one will rise, 
until the two are completely mixed. 

Ex. 50. — I will bring hydrogen to rest on 
top of air. I select two wide-mouth bottles, 
each holding about 200 cc, one with a neck 
a little smaller than that of the other, so Fig - 39 - 

that they may be put together, as in Fig. 39. The upper 
bottle is to be filled with hydrogen, the lower one with air. 

To Fill the Bottle with Hydrogen. — I first fill it to 




76 



CHEMISTRY OF THE ATMOSPHERE. 



the brim with water ; cut a piece of heavy blotting-paper a 
little larger than its mouth and slide it on as a cover and 
smooth it down closely upon the glass (Fig. 40, a). I grasp 
the bottle and turn it bottom upward over the pan, B, 
lower it into the water, remove the paper cover, and 
stand the bottle bottom upward in the water. The press- 
ure of the atmosphere will safely hold the water in the 
bottle while I invert it, and while its mouth is under water 
in the pan. 

I now put a few clippings of zinc into a side-neck flask 
and fix the flask in the clamp, then join one end of a 




Fig. 40. 

rubber tube to the side-neck, the other to a glass tube 
which reaches into the water of the pan. I pour some 
dilute hydrochloric acid (half water) into the flask and cork 
the neck at once. As soon as the air is driven out of the 
flask I put the end of the glass tube under the mouth of 
the bottle, 1 and collect the hydrogen as shown in Fig. 40. 

1 A little shelf for the bottle to stand on may be made by bending 
the ends of a strip of sheet-iron down to serve as feet to stand on the 
bottom of the water-pan. 



CHEMISTRY OF THE ATMOSPHERE. 77 

When the bottle is filled with gas I again slide the cover 
of blotting-paper under its mouth, and hold it there while 
I lift this bottle and carry it over the mouth of the other. 
I then remove the paper, and at once let the mouth of this 
hydrogen-bottle down into that of the air-bottle, as shown 
in Fig. 39. 

After waiting ten minutes I lift the two bottles, hold 
them over the water-pan, then separate them, and quickly 
put them both, mouth down, in the water. 

With a lighted match in one hand, I lift the hydrogen- 
bottle and bring the flame to its mouth ; a small explosion 
follows. I treat the air-bottle in the same way ; there 
is another explosion. These explosions show that there 
was a mixture of hydrogen and air in each bottle. 

Now air is almost 14.5 times heavier than hydrogen, and 
yet, to make that mixture, it must have risen into the 
upper bottle while the lighter hydrogen must have fallen 
into the lower one. They have mixed in spite of their 
difference in weight. 

This mingling of gases, when they are simply brought 
into contact with one another, is called the diffusion of 
gases. The difference in weight of oxygen, nitrogen, and 
carbon dioxide would arrange these gases in layers one 
above another, the heaviest at the bottom, but the principle 
of diffusion will not allow this separation; it causes all 
these gases to mix uniformly in every part of the atmos- 
phere. 

RESPIRATION. 

Animals and plants need the gases of the atmosphere as 
much as they need food and soil. Without food, an ani- 
mal starves ; without air, its death would come still more 
quickly. Pluck its roots from the soil, and a plant withers 
and dies ; give it the most fertile soil, but take away the 
air, and its death is just as certain. 



78 CHEMISTRY OF THE ATMOSPHERE. 

Both animals and plants are able to take the air into 
their bodies and then throw it out again. This act is called 
respiration. 

Respiration of Animals. — When an animal breathes, 
the air which goes to the lungs contains oxygen and nitro- 
gen, with a little of carbon dioxide, water-vapor, and still 
less of a few other gases. 

But what comes from the lungs ? Large quantities of 
water-vapor, as we know by observation, as in a cold winter 
morning, when every breath looks like a cloud of steam. 
We see the moisture of the breath at such times, because 
the cold air condenses it and makes it visible. 

But we can find this water, and something else, at the 
same time by experiment. 

Ex. 51. — I take a clean and dry bottle, cover the lower 
half of its mouth with my open lips while I pass a full 
breath into it. Notice the deposit of dew on the walls of 
the bottle. 

I next pour a few cubic centimeters of lime-water into 
the bottle and rinse the walls with it, and note the effect 
on the lime-water. 

Ex. 52. — I pour 25 cc. strong lime-water into a clean 
bottle and add 25 cc. of water. I take a glass tube, or a 
straw, and, with one end in my mouth, the other in the 
lime-water, I breathe through the transparent liquid per- 
haps two or three times. 

What is the effect on the lime-water ? 

What two substances have we found which must have 
been thrown out in the breath ? 

Now, besides the carbon dioxide and water, which we 
detect by these experiments, there is the nitrogen. The 
fact is that while the nitrogen of the air is returned to the 
air by the breath, the oxygen is used up in the body to 
make carbon dioxide and water. 






CHEMISTRY OF THE ATMOSPHERE. 79 

How is tuts brought about? — The air goes into the 
lungs, and its oxygen passes through the pores of the 
delicate membrane, of which the lungs are made, into the 
blood. With the blood, as it goes from the lungs, this oxy- 
gen is carried to every part of the whole body. It is while 
in the blood, going from place to place, that the oxygen 
meets the hydrogen and the carbon. 

But how came these to be in the blood ? Every part 
of our bodies is constantly wearing out. You cannot move 
a finger without some of its particles being worn away. 
You cannot step without some of the particles of the legs 
being worn out. Every breath, every motion, every thought, 
renders useless some portions of the parts of the body 
which are acting at the time. 

These worn-out particles are all the time going into the 
blood. They consist chiefly of hydrogen and carbon, and it 
is from these worn-out particles of our bodies that the oxy- 
gen gets hydrogen and carbon to form the water-vapor and 
the carbon dioxide which are thrown out at every breath. 

Life itself depends upon this process. These waste par- 
ticles are the impurities of the blood, and they must be 
taken out or death will quickly come. As long as oxygen 
is regularly supplied to the lungs it will change these im- 
purities into water and carbon dioxide, and in these forms 
they will be thrown out in the breath. 

These two seem to be the most abundant substances 
thrown out, but they are by no means the only ones. Many 
other impurities are exhaled at the same time. Some of 
these are very offensive, and all of them are very injur- 
ious to health if taken again into the lungs. 

Air spoiled by breathing. — Oxygen is the only thing 
in the air that can purify the blood, and this element is 
being taken from it by every breath. Once breathed, the 
air is unfit, on this account, to be breathed again, 



80 CHEMISTRY OF THE ATMOSPHERE. 

This is only one way, and that not the worst, in which 
the act of breathing spoils the air. Every breath is pol- 
luting all the air into which it is thrown, with the impuri- 
ties of the blood. Air without its oxygen would not be 
poisonous nor filthy, but air, with the abundant impurities 
thrown into it with the breath, is both poisonous and 
filthy. Were we able to see the impurities of air which 
has been breathed, we would shun such atmosphere as we 
now shun the water of a stagnant pool. Ought we to 
shun it less because they are invisible ? 

Ventilation. — It is necessary to change the air in the 
rooms of our houses very often and very thoroughly, in 
order to avoid being poisoned by our own breath. 

The removal of foul air and the introduction of that 
which is pure is called ventilation. Every room in which 
human beings are expected to live ought to have some 
means of ventilation. 

Our chemistry teaches us these facts, but chemistry is 
not left to do this alone. The same lesson is taught by 
some of the most awful experiences. 

Sometime more than a hundred years ago it happened 
that, in Calcutta, one hundred and forty-six persons were 
shut up for a night in a small room called the Black Hole. 
At dawn of day only twenty-three remained alive. 

The passengers on board a ship were all crowded into 
the cabin, one stormy night. One hundred and fifty went 
in, but only eighty came out alive. 

Examples of less painful kind are much more common. 
A schoolroom is unventilated ; the pupils become listless 
and dull from the influence of bad air. A church or hall 
is not ventilated, and a large audience becomes languid 
and sleepy. A bedroom has its doors and windows tightly 
shut ; the sleeper awakes in the morning unrested and 
with headache. 



CHEMISTRY OF THE ATMOSPHERE. 81 

These are the effects of breathing air which has already 
been breathed. 

Every building in which people are to live, even for 
short times, ought to have the means of ventilation "built 
in," but if the builder of the house has not provided some 
special means, then the windows and doors should be freely 
used for the purpose. There should be two openings in 
every inhabited room, one near the top, the other near the 
bottom. Out of one of these the foul air may escape while 
fresh air may come into the room through the other. A 
window let down a little from the top, and raised a little 
from the bottom, will meet this condition in a degree. 

The Respiration of Plants Plants breathe. They 

take air into their leaves and throw it back into the atmos- 
phere again; and this is respiration. 

The leaves are curiously made. Look at one with a 
good microscope, and w r e see that its surface is covered 
with little openings, or pores. What a multitude of them ! 
In some cases more than a hundred thousand in the small 
space of one square inch ! They are found on both the 
under and the upper side of the leaf. The air is taken 
into these little mouths on the under side, while from those 
on the upper side the gases are thrown out. 

Animals breathe in order to get oxygen from the air ; 
plants breathe in order to get water- vapor and carbon diox- 
ide. The carbon dioxide is decomposed ; its carbon is kept 
in the plant w r hile its oxygen is thrown out. While the sun 
shines this action goes on ; in the dark it does not, for it is 
found that, at night, carbon dioxide is thrown out instead 
of oxygen. 

Animals are all the time using up the oxygen of the 
atmosphere; plants are by the help of sunlight throwing 
it into the atmosphere. Animals are constantly giving 
water-vapor and carbon dioxide to the atmosphere ; plants 



82 CHEMISTRY OF THE ATMOSPHERE. 

are busy in taking these substances out. Thus do these 

two g 

other. 



two great kingdoms of nature balance and sustain eacl 



EXERCISES. 

1. Study the action of sulphuric acid on oxalic acid. 

1. Bring small quantities of the two substances together 
in a test-tube, using the concentrated sulphuric acid, and 
crystals of oxalic acid. Discover whether chemical action 
will take place in the cold, the effect of heat, whether 
a gas is set free, and any other facts you can. This work 
will suggest the next step. 

2. Proceed to collect some of the gas in order to learn 
what it is. To do this, put 5 g. of oxalic acid, in crystals, 
with 15 cc. of strong sulphuric acid into a side-neck flask, 
to make the gas ; and to collect it, arrange two conical 
flasks and one test-tube, which is fitted with a cork and 
tubes in the same manner as the flasks. 

3. Examine the gas. Put a flame into the mouth of the 
first flask to learn whether the gas is combustible or other- 
wise ; and for the name of the gas which gives the result 
you get here consult p. 46. 

Test the gas in the second flask with lime-water, and 
name the gas which this test reveals. 

Having now proved that the gas which is set free by the 
action of the two acids is a mixture of carbon monoxide 
and carbon dioxide, you can take the fourth step in your 
investigation, which is to 

Jf. Analyze the mixture. Do this by the method of 
" absorption," the same as that used in the analysis of air 
in Ex. 49. 

Fill the funnel and the rubber tube, shown in Fig. 36, 
not using the cork, with a strong solution of potassium 
hydrate. This liquid will absorb carbon dioxide, but not 



CUE MIS TRY OF THE ATMOSPHERE. 83 

carbon monoxide. Then slip the end of the rubber over 
the end of the long glass tube which passes into the test- 
tube in which you caught the gas. Put a solid stopper in 
place of the short glass tube, and then go on with the work 
as in Ex. 49. When you come to measure the volumes do 
not forget that you have used the long glass tube in the 
test-tube full of gas. 

5. Finally, write a brief account of your investigation 
and its results. 

2. Study the action of phosphorous on air. 

We have seen that phosphorus burns in air when it is 
heated (Ex. 44) ; but how will the two behave if no heat 
is used ? Remember to handle phosphorus with great care. 
See p. 67. 

1, Place a small piece of phosphorus on the end of a 
small wire, and put it into a bottle. Then invert the 
bottle and leave it standing, mouth downward, in a vessel 
of water several hours. Notice any evidence of chemical 
change or of absorption, or of any other action which may 
occur. 

2. Remove the bottle from the water without losing any 
part of what is in it, and at once test the gas which is left. 
Decide what this gas is, and then what the phosphorus 
must have done. 

S. See if you can find out, by measuring, what fraction 
of the air the phosphorus took out. 

4. Write a brief account of your work and results. 



COMPOUNDS OF NITROGEN, HYDROGEN, 
AND OXYGEN. 

We have seen that about four-fifths of the air is nitrogen 
gas, and that its effect is simply to dilute the oxygen so 
that combustion will be less furious than it would be in 
oxygen alone, and so that the air may be mild enough for 
animals to breathe. Nitrogen is just fitted to do this, 
because it has so little affinity for other elements. 

But nitrogen can be made to combine with other ele- 
ments, and in fact there are a great many of its compounds 
known. Many of these are strangely unlike the element 
itself, for while it is the mildest of all things, these com- 
pounds are among the most pungent and corrosive sub- 
stances to be found. 

AMMONIA. 

Ammonia is the compound of nitrogen and hydrogen. 

Produced in two Ways. — There are two ways in which 
these two elements can be made to combine : one is by 
electricity. If we mix the gases, and then send a silent 
electric charge through the mixture for a long time, we 
find some ammonia in the tube. 

Ammonia in small quantities is found in the air, and it 
is likely that the electricity of the atmosphere has pro- 
duced it there. 

The other way to make nitrogen and hydrogen combine 
is to bring them together just at the moment when they 
are set free from some other compounds. For example, 
they are both found in animal bodies, such as horns, hoofs, 
and flesh. Now, when these decay, the nitrogen and hydro- 
gen are set free, but they are together at the same moment, 

84 



NITROGEN, HYDROGEN AND OXYGEN 85 

and combine with one another. Neither escapes alone, but 
they go off together as ammonia. Ammonia may be fonnd 
in the air of stables, of farm-yards, and of other places 
where animal matters are decomposing. 

The Nascent State. — These gases are not the only 
things which combine most readily just at the moment 
when they are set free from something else. Other ele- 
ments also seem to be more active at that moment than 
at other times. They are then said to be in the nascent 
state. 

Formed in Gas-works. — Gas for lighting towns and 
cities is made by heating soft-coal to a cherry-red heat. 
Among the gases and vapors driven off are ammonia and 
some of its compounds. These are bad impurities, and in 
the manufacture of gas they are washed out by cold water. 
The ammonia, in this "ammonia water" of the gas-house, 
is saved by making it combine with hydrochloric acid, 
which changes it to ammonium chloride, or with sulphuric 
acid, which changes it to ammonium sulphate. This is the 
source of nearly all the ammonia and its compounds, great 
quantities of which are used annually. 

Preparation of Ammonia. — Ammonia itself is made 
by decomposing one of these com- 
pounds by heating it with lime. 

Ex. 53. — I powder a very little 
ammonium chloride and also a little 
good quick-lime. I then mix them 
well, and put into a clean and dry 
test-tube enough to half fill the 
rounded bottom. I fill the mortar 
with water colored blue by litmus, 
and add only a drop of hydrochloric Fig> 41, 

acid to redden it : let this stand ready for use when needed. 
I take the tube between my fingers, with my thumb over 





86 NITROGEN, HYDROGEN, AND OYYGEN. 

its mouth, leaving a small opening at the lower edge, and 
hold it some time in the hot air above the flame, a little 
inclined, as shown in Fig. 41. Note 

The deposits of moisture on the cold parts of the tube. 

The odor at the mouth of the tube. 

This is the odor of ammonia. 

What two substances seem to have been produced ? 

By this time the decomposition of the mixture is at an 
end, and I bring the mouth of the tube down into the red- 
dened litmus-water, still holding the tube 
so much inclined (Fig. 42) that the white 
solid will not fall down into the water. 
As the tube cools the red water rises in it. 
But it will rise much further than it would 
if the tube were heated without the mix- 
ture. (Try an empty tube in the same way, and see how 
far the water will rise.) 

What property of the gas does this show ? 
Note the change of color in the water. 
Compare this change with that in Ex. 48. 

The Facts. — We find that by heating the ammonium 
chloride with lime we get water, condensing in droplets on 
the tube; ammonia, which we know by its familiar pun- 
gent odor ; and a white solid left clinging to the bottom of 
the tube, which is calcium chloride. 

We see, too, that ammonia is a gas, but a gas which is 
soluble in water. Now the so-called ammonia in commerce 
is a liquid. It is, clearly, not the real ammonia. The fact 
is, it is water with as much as it will hold of the ammonia 
gas in solution. 

One cubic centimeter of water at 15° C. will hold 783 cc. 
of this gas, and, like all other gases, ammonia is more sol- 
uble in colder water. At 0° C. the cubic centimeter of 



NITROGEN, HYDROGEN, AND OXYGEN 



87 



water will absorb 1148 cc. of this gas. This strong solu- 
tion of ammonia is known as ammonium hydrate. 

By warming this liquid ammonia, the gas itself can be 
obtained in great abundance. 

Ex. 54. — To do this I arrange the apparatus as in Fig. 
43. I put 10 cc. or 15 cc. of the liquid ammonia in the 
side-neck flask, close its mouth 
and connect it with the short 
tube of a, whose long tube is 
joined to the short one of b. 
The stoppers must close the 
flasks air-tight. 

I put the short tube of a next 
the flask, because this gas is 
lighter than air. It will collect 
in the upper part of a, and 
push the air out through the 
long tube into the upper part Fig. 43. 

of b, and afterwards out of the long tube of b, until both 
flasks are full. 

I now make the lamp-flame very small, so that only a 
current of hot air will warm the liquid in the flask. The 
gas will soon escape freely. Some water-vapor goes over 
with it, but I use as gentle heat as I can to keep it bub- 
bling ; the water does not boil ; the bubbles are ammonia 
gas, mixed with little vapor. 

Note the odor of the gas which escapes from the open 
tube of b; it will be more and more pungent until the air 
is all out of the flask. 

Ex. 55. — Moisten a stick with hydrochloric acid and 
hold it just above the tube of b. 

What evidence of chemical action do you find ? 
Compare this with Ex. 9. 





88 NITROGEN, HYDROGEN, AND OXYGEN. 

Ex. 56. — I take both rubber tubes from a, and at once 
plunge the stoppered mouth of the flask down into a vessel 
of water (Fig. 44). 

What is the result ? 
What does it teach about ammonia 
I gas ? 

Ex. 57. — I redden some blue lit- 
Fi e- 44 - mus with as little hydrochloric acid 

as will do it, and then pour into it some of the water which 
has just now dissolved the gas in a. 

How does the ammonia show its presence in the water ? 
Has this ammonia-water any taste or odor ? 

The Facts. — Dry ammonia-gas is invisible and much 
lighter than air. Its solution in water has a caustic taste, 
and will bring back the blue color of litmus which has been 
reddened by acid. 

Ammonia is a stimulating gas to breathe : on this ac- 
count it is used to revive the faint, and sometimes to 
overcome the effects of an anaesthetic, like ether or chlo- 
roform. 

Ammonia and hydrochloric acid combine at once, when- 
ever brought together, and form ammonium chloride. The 
white cloud in Ex. 55 was a cloud of ammonium chloride. 

Ammonium Salts. — Ammonia acts also on other acids, 
and so forms a large number of compounds, which as a 
class are called ammonium salts. 

Ex. 58. — I put 10 cc. of water into a small wide-mouth 
bottle and add 2 cc. strong sulphuric acid. I place this in 
a porcelain dish and drop into it a small clipping of blue 
litmus-paper. 1 I now add strong ammonia water (ammo- 
nium hydrate) little by little, shaking the mixture well 

1 Filter-paper soaked in a strong solution of litmus and afterward 
dried. 



NITROGEN, HYDROGEN, AND OXYGEN. 89 

each time, until the red paper turns blue. If now I add 
drop by drop of the dilute acid, I can reach the point 
when the paper is just reddened by the last drop, and 
when another drop of ammonia will make it blue again. I 
do this. And then I put the dish over a small flame and 
evaporate (Fig. 10) the liquid, until a white rim is seen 
around its edge on the dish, and then let it cool. 

While waiting for the liquid to evaporate I begin the 
next experiment. 

Ex. 59. — I mix 5 cc. of water and 5 cc. strong nitric 
acid, add the blue litmus-paper and then the ammonium 
hydrate, until the last drop turns the paper blue. I then 
evaporate this liquid to about one-fourth its bulk, and let 
it cool. 

If the liquids were evaporated enough, crystals of a white 
solid will be seen in each when it is cold, or the whole may 
become a solid white mass. 

Ex 60. — I take a little of one of these white solids to 
test its action on litmus. I first pour upon it, and then 
quickly off again, a little water — just to wash it. And 
then I add water to dissolve it. I take two clippings 
of blue litmus-paper, moisten one with water, and then 
redden it by holding it in the mouth of the bottle of 
hydrochloric acid, and then put both into the solution. 
No change of color should occur in either. 

These white solids, made by the action of ammonia on 
sulphuric and nitric acids, are examples of ammonium 
salts. 

But why did we use the litmus ? Simply to show 
when the chemical change was ended. We have found 
that blue litmus is reddened by an acid in every case, and 
that ammonia will bring back the blue color. But when 
there is just enough ammonia to use up all the acid, 



90 NITROGEN, HYDROGEN, AND OXYGEN. 

neither the blue nor the red is changed. The ammonia 
and the acid neutralize each other, and the litmus shows 
the end of this action. 

Do not leave this until you see clearly why the two neu- 
tralize each other. Consult p. 57 for the law. 

Composition of Ammonia by Volume It is found 

by analysis that ammonia always yields just three times 
as many cubic centimeters of hydrogen as of nitrogen. 
Its composition by volume is : 

3 measures hydrogen to 1 measure nitrogen. 

But another question is, How much ammonia gas would 
these 3 of hydrogen and 1 of nitrogen make ? It has been 
found by analysis that 20 cc. of ammonia will give 30 cc. 
of hydrogen and 10 cc. of nitrogen. That is to say, 30 cc. 
of hydrogen and 10 cc. of nitrogen make 20 cc. of am- 
monia. 

Three measures of hydrogen and one measure of nitro- 
gen make two measures of ammonia. Or four volumes of 
the constituents are condensed to two volumes of the 
compound. 

Compare this curious fact with another noted under the 
composition of water, p. 56. 

NITRIC ACID. 

Nitric acid is a compound of nitrogen, hydrogen, and 
oxygen. It is one of the strongest of acids, and one of 
the most useful. 

Occurs in Combination. — Very small quantities of 
this acid exist, free, in the air: it is in its compounds that 
it is mostly found. Two of these compounds occur in large 
quantities in some parts of the earth : they are " saltpetre," 
whose true name is potassium nitrate, and "Chilian salt- 
petre," or sodium nitrate. 



NITROGEN, HYDROGEN, AND OXYGEN 91 

Made from Sodium Nitrate. — To get the nitric acid 
the sodium nitrate is heated with sulphuric acid. Sulphu- 
ric acid is still stronger than nitric acid, and will drive the 
latter out of the nitrate in order to take its place. The 
nitric acid is driven out in the form of vapor, but it is 
carried into a cold vessel, where the vapor is condensed 
to a liquid. 

Properties. — Nitric acid when pure has no color, but 
it is intensely sour and very corrosive. It will redden 
litmus like other acids, but will not stop with this : it will 
go right on to destroy the red color. Try this by putting 
a piece of litmus-paper into a little of the strong acid. 
It will first turn red, soon afterward yellow, and in a little 
time the paper will easily break to pieces. In the same 
way it will form yellow stains upon the fingers, and upon 
the garments, and, in fact, upon all organic bodies. The 
acid may be washed away by water, or it may be neutral- 
ized by ammonia, but the yellow color will remain. 

Ex. 61. — Wet some pieces of woolen cloth with drops 
of nitric acid, with drops of hydrochloric acid, and of 
sulphuric acid. Wait until the color is changed by all, 
and then try the effect of ammonia on them. Note the 
difference. 

The strong nitric acid in commerce is by no means pure : 
in fact, it is almost half water, and there are several other 
impurities besides water, in small quantities. By distil- 
ling a mixture of this acid with strong sulphuric acid the 
pure and concentrated nitric acid is obtained. 

Decomposition of Nitric Acid. — This acid is very 
easily decomposed. It is decomposed by light. When 
standing in the sunlight, the upper part of the bottle of 
acid will, after a time, be seen full of a reddish vapor; 
this is set free from the acid by light, and water is 
formed at the same time. The yellow color of the com- 



92 NITROGEN, HYDROGEN, AND OXYGEN. 

mon acid is due to this reddish vapor, some of which 
is dissolved in the liquid. 

The Nitrates. — Nitric acid is easily decomposed by 
almost any metal. Cue can see this action by putting 
small bits of copper or lead in a test-tube and covering 
them with dilute nitric acid. But the fumes are very nox- 
ious, and the experiment should be made on a small scale, 
or else in the open air. The same red vapor, seen when 
the acid is decomposed by light, is set free in abundance 
by the metal. Water is also formed, and beside these a 
salt of nitric acid is produced. These salts of nitric acid 
are called nitrates. The salt made with copper is blue, and 
it is called copper nitrate ; that made with lead is white, 
and is called lead nitrate. 

This decomposition of nitric acid by a metal will be 
better understood further on, when we study Ex. 62. 

These nitrates are all soluble in water, and so when a 
metal is changed into a nitrate the metal seems to dis- 
solve, but it is always the nitrate which is in solution, and 
not the metal. 

Aqua Eegia. — Nearly all the metals are thus changed 
into nitrates by nitric acid ; but gold and platinum are the 
exceptions. To dissolve these metals we. need a mixture 
of nitric and hydrochloric acids. Neither of these alone 
can attack gold or platinum, but the two together will 
dissolve them readily. The mixture of these two acids 
is called aqua regla. But, as we shall see, the metals 
dissolved in aqua regia are not changed into nitrates, but 
into compounds of chlorine, called chlorides. 

NITROGEN OXIDES. 

Investigate the Decomposition of Nitric Acid 

We have just seen that when nitric acid is decomposed 
reddish vapors are set free. What are these vapors ? 




NITROGEN, HYDBOGEN, AND OXYGEN. \)6 

Let us study the action by experiment. We will decom- 
pose the acid by copper. 

Ex. 62. — I fit up my apparatus for making and collect- 
ing gases as usual for a 
gas heavier than air (Fig. 
45), the long tubes of the 
flasks a, b, c toward the 
side-neck flask. Into both 
a and b I put water, which 
the cut shows only in 
a, but none in c. After 
the connections are made, 
I put about seven grams 
of small pieces of copper- 
foil, or thin sheet-copper, Fig. 45. 
in the side-neck flask, pour in about 25 cc. of dilute nitric 
acid, half water, and close the flask with its air-tight stop- 
per. The chemical action sets in at once. No heat is 
needed to start it. 

Note the change in the color of the acid. 

Trace the changes of color as they occur in s, a, b, c. 

We*see that a red gas quickly fills the flask s, and goes 
over into a, b, c, but that the red color disappears from 
s, a, and b, and stays in c for a much longer time. 

How many kinds of gas are evidently in the flasks ? 

When a and b are clear, and c still full of red-brown gas, 
I disjoin the rubber tube of c, remove the stopper carefully, 
pour in gently a few cubic centimeters of water, and return 
the stopper to its place as tightly fitted as before. I now 
close the ends of both glass tubes with my finger, which I 
can easily do if they are at the same level, lift the flask 
and shake it well. Note the disappearance of the red gas. 
I next plunge the finger and tubes under water, and -take 
the finger away. Note the inrush of water. 



94 



NITROGEN, HYDROGEN, AND OXYGEN 



Why did the color of the gas disappear with water ? 

Why did the water rush in when the tubes were opened ? 

What property of the red gas is thus discovered ? 

Ex. 63. — I now disjoin the rubber tubes of b, and then 
invert the flask and let the water run out of the short tube. 
Of course air will run in through the long tube and mix 
with the colorless gas within. The red gas is reproduced ! 

This is an important discovery. If air will change the 
colorless gas into the red gas, perhaps it was in this way 
that the red gas was made in the flasks at first, for they 
were full of air when the action began in s. If I could 
keep the air away, while the copper and nitric acid act on 
each other, would the red gas appear at all ? 

Now I can keep the air away, and answer this question, 
by putting carbon dioxide into the flasks in place of the air. 

Ex. 64- — I disjoin the rubber tubes of a, and empty the 
contents of s into a porcelain dish to be examined after- 
ward. I then join the side-neck 
with the long tube of another 
flask (Fig. 46). I put 20 cc. 
dilute nitric acid, half water, 
into s, drop in gently two or 
three pieces of marble as # large 
as peas, and close the flask. Car- 
bon dioxide will be set free, 
drive the air before it out at 
the open short tube, and will 
ft soon fill the flask. I then open 
Iis - 48, s, drop in some bits of copper, 

and quickly close it again. The nitric acid and copper now 
act in the absence of air. Do they yield the red gas ? 
None will be seen if the air was all expelled. Do they 
yield the same colorless gas as before ? I mix air with the 
gas in e ; the red gas instantly appears, as it did in Ex. 63. 







NITROGEN, HYDROGEN, AND OXYGEN. 



95 



Our experiments clearly prove that when copper decom- 
poses nitric acid, only a colorless gas is set free. But 
when this colorless gas meets with air, another, a red- 
brown gas, is formed. At the same time a blue compound 
is made which stays in the liquid. The colorless gas is a 
compound of nitrogen and oxygen, called nitric oxide, and 
the red-brown gas is another compound of nitrogen and 
oxygen, called nitrogen peroxide. The blue compound is 
copper nitrate. It may be obtained in blue crystals by fil- 
tering the liquid and evaporating it until, on cooling, the 
crystals form. (Try it.) 

When nitric oxide mixes with air it instantly combines 
with oxygen and becomes nitrogen peroxide. 

Nitrous Oxide. — There is another compound of nitro- 
gen and oxygen called nitrous oxide. It is not usually 
made by the decomposition of nitric acid directly, but by 
decomposition of ammonium nitrate, and this is done by 
means of a gentle heat, which breaks the nitrate into water 
and nitrous oxide. Thus : 



- 1 put from 7 to 10 grams of ammonium nitrate 
side-neck 



Ex. 65. 
into the 

flask, which should 
be dry, and join the 
flasks a, b, c, as usual 
for a heavy gas. To 
condense the steam, 
I put the empty flask 
a into a dish of cold 
water, — ice-water is 
best. It may be held 
down in the water by 
a cord passing over 
the stopper and around under the heavy dish of water. To 
decompose the nitrate I use the gentle heat of a small 




Fig. 47. 



96 NITROGEN, HYDROGEN, AND OXYGEN 

flame, just hot enough to melt and keep it gently boiling. 
The nitrate slowly wastes away, and when but about one- 
fifth remains I withdraw the lamp. 

Flasks s and a prove that water is produced. How ? 

Test the gas in b with the flame of a splinter of wood. 

Note the color, and the odor, of the gas in c. 

The Facts. — Ammonium nitrate contains nitrogen, hy- 
drogen, and oxygen, and when it is decomposed the nitro- 
gen and hydrogen separate, each taking a part of the 
oxygen with it. The nitrogen and oxygen form the nitrous 
oxide, while the hydrogen and oxygen form water. The 
water is condensed in a (Fig. 47), while the nitrous oxide 
is collected in a, b, and c. 

Nitrous oxide is a colorless gas in which bodies will burn 
with almost the same vigor as in oxygen itself. But its 
most remarkable action is upon a person who breathes it. 
Breathed in small quantities it intoxicates, and often causes 
a disposition to laughter. On this account it is commonly 
known as laughing-gas. But if its use be continued a few 
minutes, it will produce complete insensibility, and if con- 
tinued, death. It is much used to render patients insensi- 
ble to pain in minor surgical operations, such as the extrac- 
tion of teeth. The insensibility lasts a few minutes only ; 
it is quickly banished by fresh air. 

The Five Nitrogen Oxides. — There are two other 
compounds of nitrogen, making in all five. Here are five 
entirely different kinds of substance made out of the 
same two elements. But how can the same elements make 
different compounds ? By combining in different propor- 
tions. When the colorless nitric oxide touches the air it 
takes in more oxygen and becomes the red nitrogen per- 
oxide. Different weights of these elements unite. 

Let N stand for nitrogen and for oxygen. By analy- 
sis it has been found that 



NITROGEN, HYDROGEN, AND OXYGEN. 97 

Nitrous oxide contains 28 of X and 16 of 
Nitric oxide " 14 " " " 16 " " 

Nitrogen peroxide " 28 " " " 48 " " 
Nitrous anhydride " 14 " " " 32 '" " 
Nitric anhydride " 28 " " " 80 " " 

The properties of a compound depend on the relative 
weights of the elements in it. This fact is clearly shown 
by these nitrogen oxides. 

The Law of Multiple Proportions It is a curious 

fact that the relative quantities of oxygen in this table of 
nitrogen oxides are all either 16, or else 2 or 3 or 5 times 
16. So, too, in the case of the nitrogen the quantities are 
either 14, or twice 14. In both cases alike, the larger 
numbers are all exact multiples of the smallest. Now 
chemists have found this to be true in a great many other 
cases where two elements make more than one compound. 
In fact they have met no exception. This causes them to 
feel quite sure that all elements are alike in this respect, 
and they state this conclusion as follows : 

If one element combines with another in more than one 
proportion, these proportions are all exact multiples of some 
one fixed number. 

And this important statement of fact is known as the 
"law of multiple proportions." The student should now 
remember the "law of constant proportions" (p. 57), for 
these two laws together cover the most vital facts about 
the combination of elements. 

Combination of Definite Weights. — These two laws 
show very clearly that the elements never combine except 
in certain definite weights. 

The definite weights of oxygen and hydrogen in water 
are in the ratio of 16 to 2. Sixteen grams of oxygen and 
two grams of hydrogen will unite without leaving any of 
either. But if we pass an electric spark through a mixture 



98 NITROGEN, HYDROGEN, AND OXYGEN 

of 16 g. of oxygen with 3 g. of hydrogen, just 1 g. of hydro- 
gen will be left. 

The definite weights in which oxygen and nitrogen 
always combine have the ratio of 16 to 14. 

The definite weights of hydrogen and chlorine which 
make their compound, hydrochloric acid, are as 1 to 35.5. 
In other compounds of chlorine the definite weight of 
chlorine used may be 2 or 3 or some other whole number 
of times 35.5. And in other compounds of hydrogen the 
definite weight of hydrogen may be 2 or 3 or some other 
whole number of times 1. 

Combining Weights. — These numbers which show the 
ratios of the smallest definite proportions by weight in 
which these elements ever combine with anything else, 
are called combining weights. Thus we say 



The combining weight of Hydrogen is 


. . 1 


" " " " Oxygen " . 


. . 16 


" " " " Nitrogen " . 


. . 14 


" " " " Chlorine " . 


. . 35.5 



And we mean that the smallest weight, of chlorine for 
example, which we can find in any compound is just 35.5 
times as large as the smallest weight of hydrogen which 
can be found in any of its compounds. 

To find these numbers — the combining weights — is one 
of the most difficult problems in chemistry. The student 
is not yet ready to see how it is done. But it has been 
done for the whole list of elements. Every element has a 
combining weight assigned to it. 

EXERCISES. 

1. Make some JSfessler's reagent as follows : 

1. Make a solution of potassium iodide, say 6 g. in 20 cc. 
of distilled water, or of the best spring water, 



NITROGEN, HYDROGEN, AND OXYGEN. 99 

2. Make a strong solution of mercuric chloride, say 6 g. 
in 60 cc. of water. 

3. Add the mercuric chloride solution, little by little, to 
the potassium iodide, until a small portion of the precipi- 
tate will not disappear when shaken or stirred. 

Jt. Make a strong solution of potassium hydrate, say 
10 g. in 15 cc. of water, and when cold add this to the 
mixture already made. 

Finally, let this mixture stand until it is perfectly clear. 
The clear liquid is called Nessler's reagent. 
2. Study the effect of Nessler*s reagent on solutions contain- 
ing ammonia. 

1. Add a drop or two - of ammonium hydrate to a test- 
tube nearly filled with distilled or spring water. Then add 
1 cc. of the Nessler's solution. Mix it well, and note the 
color of the mixture. 

Find out whether less than a drop of ammonia will yield 
this color in the same quantity of water. Or how little 
you can use and still be able to detect the color. 

2. Put a little solution of ammonium chloride in the 
water, instead of ammonia, and test it with the Nessler's 
solution. 

Does the ammonia of the ammonium chloride yield the 
same color ? 

The fact is that Nessler's solution is the most delicate 
test for ammonia, always showing the presence of that sub- 
stance by a yellow color, which has a light straw tint 
when very little ammonia is present, and a deep orange 
tint when there is much. 

3. Learn by this test whether rain-water contains am- 
monia. 

Why should rain-water contain ammonia ? 
4- Test the drinking-water of the neighborhood for am- 
monia. 



100 NITROGEN, HYDROGEN, AND OYYGEN 

3. Study the effect of nitric acid on ferrous sulphate, some- 
times called "copperas" 

1. Into a little dilute nitric acid in a test-tube drop a 
good crystal of the ferrous sulphate. Do not shake it. 
Notice the color which appears in the liquid around the 
crystal. 

2. See how dilute you can make the acid and still be 
able to detect this color when a crystal of the sulphate is 
used. 

3. Try the solution of a nitrate, say potassium nitrate, 
instead of nitric acid, in the same way. 

Does the color now appear around the crystal ? If not, 
there is probably little or no free*nitric acid present. 

If. Mix a little solution of the potassium nitrate with a 
solution of. the sulphate, incline the tube, and let a little 
concentrated sulphuric acid run down the inside of the 
glass, to the bottom. Do not shake it. 

The color should now appear as a ring, where the liquids 
touch each other. 

If so, then why did it not in the other case ? 

The fact is that strong sulphuric acid decomposes the 
nitrate and sets its nitric acid free. And then the free 
nitric acid shows itself by the color it makes by acting on 
the crystal. 

5. Make the experiment again with potassium nitrate 
and sulphuric acid, but add the ferrous sulphate to the 
liquid when hot. 

Ferrous sulphate is a delicate and much-used test for 
nitric acid and the nitrates. It must be used in cold solu- 
tions : the brown color disappears on heating. 

6. Get a little of some white solid, the name of which 
you do not know, from the teacher, or a friend who knows 
what it is, and see if you can tell by the copperas test 
whether it is a nitrate or not. 



THE COMPOSITION OF PLANTS. 

The substances which exist in plants, or which may be 
made from them, are so many that we cannot undertake 
to study them all. The most that we can do now is to 
ascertain the elements of which plants are made, and per- 
haps a few of their simpler compounds. 

Let us examine a piece of wood as follows : 

Ex. 66. — I take a splinter of well-dried pine wood, 
about as large and long as a common match, drop it into a 
test-tube, and then heat it slowly by holding the tube 
almost horizontally just above the tip of the lamp-flame, 
and move the tube back and forth to heat the length of the 
wood. 

Notice the dew on the cold walls ; what does this show ? 

Notice the vapors ; do they condense or go off as gases ? 

Notice whether any other liquid than water is formed. 

Describe the stick after the changes are over. 

The Facts. — When wood is heated in a close vessel, 
where there is not air enough to burn it, there are many 
new products of its decomposition. Some are gaseous ; 
these escape into the air. Some are liquid; these con- 
dense on the cold parts of the vessel. A black solid is 
left which no heat seems to affect. Among the liquid 
products is water, — the dew seen on the walls of our 
tube ; and the black solid which was left behind is char- 
coal, which is the element carbon, almost pure. But water 
is always made up of hydrogen and oxygen, and as water 
comes from the well-dried wood, the wood must contain 
these elements also. Thus we prove that wood contains 
carbon, hydrogen, and oxygen. 

101 



102 COMPOSITION OF PLANTS. 

By extending our experiments to other kinds of vege- 
table matter we find in them the same elements : carbon, 
hydrogen, and oxygen. Every blade of grass, every leaf 
and flower, and every kind of seed and fruit, contain these 
three elements, and they contain very little of any others. 

Plants do indeed contain other elements than these. 
Nitrogen is found in them ; in small quantities to be sure, 
but it must not be overlooked, because it is one of the most 
important elements in the vegetable food of animals. 

Besides nitrogen there are several other elements in 
minute quantities, which, with carbon, hydrogen, and oxy- 
gen, enter into the composition of plants. 

When wood or any other vegetable matter is burned, 
these four elements disappear, and nothing but a little 
ash remains ; but this ash contains all the other elements 
of the substance. How small the quantity ! It seldom 
amounts to one tenth of the whole. In every 100 pounds 
of vegetable matter, from 90 to 97 pounds are made up of 
carbon, hydrogen, oxygen, and nitrogen. All these facts 
have been established by experiments. 

The Food of Plants. — An animal, to live and grow, 
must be supplied with food. The same is true of plants : 
they must be supplied with nourishment which contains 
all the elements they need to promote their growth. Now 
carbon, hydrogen, and oxygen, with a little nitrogen, and 
very small quantities of a few other elements, make up 
every part of any plant. These the plant must get in 
some way, else it cannot flourish. If any of them are 
lacking, the plant suffers even if it does not die. The 
food of plants must contain all these elements. 

The plant gets its carbon from carbon dioxide. It gets 
its hydrogen and oxygen from water. It gets its nitrogen 
from ammonia, and as nine-tenths of the weight of 
plants is made up of carbon, hydrogen, oxygen, and nitro- 



COMPOSITION OF PLANTS. 103 

gen, it is easy to see that the three substances just named 
must be the food upon which plants must chiefly live. 

But how can a Plant take Food? — Every plant has 
a multitude of mouths. There is one at the end of every 
little rootlet in the soil, and there are a host of them 
on the under side of every leaf. Each little root-mouth 
of a growing plant is taking in liquid food from the soil, 
and each little leaf-mouth is at the same time taking 
gaseous food from the air. 

The liquid which enters the roots of a plant is water 
in which many substances of the soil are dissolved. It 
contains compounds of ammonia, from which the plant can 
get nitrogen, and it also furnishes the plant with those 
other elements which it needs in small quantities, those 
which make up the ash which is left when the plant 
is burned. 

The gaseous food which enters the leaves of a plant 
is the carbon dioxide and water-vapor of the air. From 
these gases the plant gets carbon, hydrogen, and oxygen, — 
the three most abundant elements needed in its growth. 

The food of plants must be decomposed before its carbon, 
hydrogen, oxygen, and other elements can nourish them. 
These elements then combine again in very different ways 
to produce all the materials of which the parts of a plant 
are made, such as starch, sugar, wood-fiber, gums, oils, and 
coloring matters. 

Among the four chief elements in plants, the only one 
which we have not studied is : 

CARBON. 

The Source of Carbon in Plants. — Carbon dioxide 
is one of the most important substances in the food of 
plants. But the oxygen of this substance is of no use 
to them ; they get enough of that from other sources ; 



104 



COMPOSITION OF PLANTS. 



it is the carbon which is useful. Now, every leaf of a 
growing plant is taking the carbon dioxide of the air 
which passes over it. We learned this when studying 
the subject of respiration. This substance is decomposed 
while in the leaf ; its oxygen is exhaled, but its carbon 
remains to enter into combination as a part of the body 
of the plant. 

Charcoal-making. — This carbon, which the plant has 
taken from the atmosphere, and also the little which 
it may have taken up through its roots, is obtained without 




Fig. 48. 

much difficulty, for use in the arts, and we are acquainted 
with it under the name of charcoal. 

The charcoal-maker piles his sticks of wood in the form 
of a mound, and covers the whole with dirt and turf. He 
leaves a few small holes for a little air to enter the pile 






COMPOSITION OF PLANTS. 105 

at the bottom, and another at the top for the smoke to 
escape, and in this way a half-smothered burning is kept 
up for a long time, as shown in Fig. 48. 

Now what change occurs ? A very simple one. The 
wood is decomposed by the heat ; its gaseous constituents 
an 1 driven away, but its solid carbon is left behind. Not 
all of it, to be sure, for a little of it unites with oxygen 
and flies away as carbon dioxide. But the carbon which 
is lost in this way is very little compared with the char- 
coal which is left. 

In appearance, the wood only seems to have changed in 
color. It is black. In other things the charcoal looks like 
the wood. There is the bark with all its knotty roughness. 
There are the annual rings inside the bark, to be plainly 
counted, and, if we look through a microscope, there are 
the delicate cells, which the microscope could have shown 
us in the wood before it was burned. Let us lift it, and 
it is easy to feel that the wood has lost much of its weight, 
but really it is not easy to see that it has lost much of 
its size ; the stick of charcoal is very nearly as large as 
the stick of wood from which it was made. 

Charcoal is xot quite Pure Carbox. — When pure 
carbon burns it is wholly changed into carbon dioxide gas ; 
no solid ash remains, but charcoal always leaves a little 
ash, which proves it to be impure carbon. 

Other impure Forms resembling Charcoal. — -Char- 
coal is only one of the many common forms of carbon. 
Among those most nearly like charcoal we may mention 
now the hard coal, which is taken from mines for fuel; 
coke , the black and porous solid left in the retorts of 
gas-works; bone-black, obtained by heating bones in close 
vessels ; soot, to be found in chimneys ; and lamp-black, 
so much used in the manufacture of printing-ink. 

Lamp-black. — Lamp-black is made by burning pitch 



106 



COMPOSITION OF PLANTS. 



or tar with little air. The pitch is put into an iron pot 
and heated as shown at the left in the cut (Fig. 49). A 

dense black smoke 
is carried by the 
draught over into 
a large chamber. The 
blackness of this 
smoke is due to fine 
particles of carbon. 
This substance col- 
lects on the walls of 
the chamber, and is 
afterwards taken out 
as a fine black powder. 
This is lamp-black. 

Printers' ink is a 
mixture of lamp- 
black and oil ; every 
printed mark on this 
page is a thin layer 
of carbon clinging 
tightly to the paper. 
Action of Charcoal on Gases Charcoal is very por- 
ous, and has remarkable power to absorb gases. Let us 
study this action by experiment with ammonia. 

Ex. 67. — I must first heat the charcoal to redness to 
drive out the air already in it. I select a piece that has 
been well burned, make it about one inch long, and small 
enough to slide easily into my graduated cylinder. I place 
it in the bottom of my porcelain dish, or better, in a large 
iron spoon, cover it completely with fine sand, and put it 
in a good fire. After it has been heated to full redness 
for some time I let it cool, still protected by the sand. 
While the spoon is cooling I fill my cylinder with am 
nionia gas ? in this way : 




COMPOSITION OF PLANTS. 



107 




Place the cylinder, inverted, through the ring of the sup- 
port. Pour 5 cc. liquid ammonia into the side-neck tube, 

and put the delivery 

tube up into the cyl- 
inder. Then gently 

heat the liquid. I 

can hold it by means 

of a strip of paper 

which I wind around 

it, as shown in Fig. 

50. Ammonia gas 

w T ill be driven over 

into the cylinder, 

and, being little 

more than half as Fig. 50. 

heavy as air, it will rise to the top and gradually expel the 

air until the cylinder is filled. 

I now place the cold charcoal in the mouth of the cylin- 
der and then quickly lower it into a dish 
of mercury. If the mercury rises in the 
cylinder, as in Fig. 51, it will prove that 
the ammonia gas is being absorbed by the 
charcoal. 

Facts. — Charcoal will take up 90 times 
its own volume of ammonia gas, but only 
8 or 9 times its volume of oxygen or nitro- 
gen or carbon dioxide. This remarkable 
power of charcoal makes it very useful in 
hospitals and other places where offensive 

odors are to be found. It will absorb the bad gases, and 

thus purify the air. 

Even animal substances, when decaying, lose their power 

to offend us by their odor, if covered with a layer of good 

charcoal. The decay will go on, but the odor will be lost. 




Fig. 51. 



108 



COMPOSITION OF PLANTS. 



Action of Charcoal on Colors. — Charcoal also has 
the power to absorb many coloring matters. Animal char- 
coal, or bone-black, possesses this property in higher degree 
than wood charcoal. 

Ex. 68. — I prepare a filter, and rest the funnel in the 
month of the cylinder. I fill the filter nearly full of bone- 
black. Finally, I pour upon it some water colored with 
blue litmus. If it comes through still colored, I pour it 
back and let it run through a second time. Is the color 
removed ? It has been absorbed by the charcoal. 

Ex. 69. — In the same way I filter some water colored 
with cochineal. 

Ex. 70. — I try a solution of dark brown sugar. 
Ex. 71. — I try a solution of potassium chromate. This 
is a mineral coloring-matter ; the others have been organic. 
Is the color discharged in all these cases ? 
Applicatiox. — This power of charcoal makes it very 
useful for taking the color out of liquids. Great quantities 

are used to remove the 
brown color from crude 
sugar. After passing 
the dark syrup through 
a charcoal-filter it is 
bright and colorless. 

Charcoal filters are 

much used to purify 

drinking-water. The 

charcoal gradually loses 

its power as its pores 

Flg " 52, are more and more 

filled with the impurities. Fresh portions should then be 

put in its place, or the same portion may be again heated 

to redness, which will restore its power. 




COMPOSITION OF PLANTS. 109 

Action of Charcoal on Oxides. — Charcoal has a strong 
attraction for oxygen, and when very hot it will decompose 
many compounds of oxygen in order to unite with it. 

Ex. 72. — I make a mixture of 1 g. copper oxide with 
about its own bulk of powdered charcoal, put it into the 
side-neck ignition-tube, and place the end of the delivery 
tube in some lime-water contained in a test-tube, as shown 
in Fig. 52, and then apply the heat of the Bunsen lamp. 

What is the effect on the lime-water ? 

What, then, was the gas produced by the action ? 

What are the elements of this gas ? 

In what form were these elements in the mixture ? 

Can you see any change in the black copper oxide ? 

What, then, must have been the action of the carbon ? 

The Facts. — The black copper oxide is composed of 
copper and oxygen, but when heated the carbon takes the 
oxygen away from the copper and unites with it to form 
carbon dioxide. This leaves the copper free. The carbon 
dioxide whitens lime-water. The copper left behind should 
appear distinctly reddish in the tube. 

This power of carbon to decompose oxides makes it very 
useful in the work of getting metals out of ores. Iron, for 
example, is found in the mine in the form of iron oxide, 
and by mixing this ore with coal, and then heating it 
intensely in a furnace, its oxygen is taken away by the 
carbon, and the iron is left in the metallic form. 

The Diamond. — The diamond, most brilliant of gems, 
is nothing but carbon. It is crystallized carbon. Dull, 
black charcoal, very common and very cheap, and the beau- 
tiful diamond, most costly of precious gems, are only two 
different forms of the same element. 

The diamond is the hardest known substance. It can- 
not be cut or even scratched by any other. Very small 



110 



COMPOSITION OF PLANTS. 



and otherwise useless diamonds are set in the end of a 
proper handle and are commonly used for cutting glass. 

When found in the earth the diamond has the shape and 
appearance of a roughly rounded pebble. This rough gem is 
" cut " into one of two principal forms of jewel. They are 
called the brilliant and the rose. The first of these is re- 
garded as the finest. Its shape is well shown in Fig. 53. 

Look at the gem sidewise, 
and it appears as seen in 
the upper part of the pic- 
ture ; look at the top of 
it, and it appears as seen 
in the lower part. The 
form of the rose is seen in 
Fig. 54 ; a side view above 
and a top view below. 

Graphite. — Another 
form of carbon is known 
under the common name of 
black-lead, and is very fa- 
miliar to us in its most 
useful shape, the lead of 
our lead-pencils. This 
name does not belong to 
it properly, for it is not 
lead. It has no proper- 
ties like those of lead ex- 
cept that which allows it 
to leave marks upon paper. It is sometimes called plum- 
bago ; but the name by which it is generally known in 
chemistry is graphite. 

Graphite is found in the earth. It is as black as coal, 
but it has a dull shining appearance, which coal has not. 
It is among the softest minerals to be found, and as per- 




Fig. 53. 



COMPOSITION OF PLANTS. 



Ill 



feetly opaque as can be. How unlike the hard and trans- 
parent diamond in these respects ! 

Three Forms of the Same Element. — All three of 
these forms of carbon are alike in some respects. No fire 
can melt them. No liquid can dissolve them, if Ave except 
melted iron, which seems to dissolve a little carbon. They 
cannot be changed by exposure to the atmosphere ; they 
suffer no decay, no rust. But let them be heated hot 
enough, where oxygen is 
present, and they will burn, 
and the experiment shows 
that they are not only much 
alike in some respects, but 
that they are actually the 
same kind of matter, 

For we have proved by 
experiment, that when char- 
coal burns carbon dioxide is 
produced. By heating the 
diamond to a white heat, in 
oxygen gas, it will be con- 
sumed, and carbon dioxide 
will be found in its place. 
Graphite has also been 
burned, and the same substance, carbon dioxide, produced 
by its combustion. 

Now we know that it takes carbon and oxygen always, 
and nothing else, to make carbon dioxide. The carbon 
must come from the fuel which burns. Hence charcoal, 
diamond, and graphite are all the same element, — carbon. 

What other element have we found to exist in more than 
one form ? Wfrat name is given to this property of ele- 
ments ? 

How this element has come to be in such wonderfully 




Fig. 54. 



112 



COMPOSITION OF PLANTS. 



different forms we cannot tell. No chemist can change 
charcoal into diamond; nor can any One tell us how it has 
been done in the great laboratory of nature. 

CARBON DIOXIDE. 

Preparation. — Carbon dioxide is the chief compound of 
carbon and oxygen. It is most easily obtained by the 
action of hydrochloric acid on marble. 

Ex. 73. — My apparatus is much the same as that used 
in making oxygen (Ex. 23). It is shown in Fig. 55. A 

little lime-water is 
placed in the bottle 
d, and clear water 
in a, enough to 
cover the end of the 
glass tube. The 
conical flasks are 
joined by rubber 
tubes, the long tube 
in each to the short 
tube of the one be- 
fore it, and then 
Fi s- 55 - the long tube of a 

to the side-neck of the flask s. The joints are all air-tight. 
I put about 10 g. of marble in small pieces into the side- 
neck flask and pour upon it about 25 cc. of dilute hydro- 
chloric acid, half water, and at once close the flask with its 
stopper. The gas, making in s, will drive the air before it 
all out at d. The flame of a burning splinter thrust into d 
will tell when the bottle is full of the carbon dioxide. 
Then exchange this bottle for another having some blue 
litmus-water instead of lime-water. 

If the gas begins to come too slowly, I ma}^ remove the 
cork of s 3 add more acid, and replace it. Now consider 
the following things : 




COMPOSITION OF PLANTS. 



113 




Describe the action which took place in s. 
What effect was produced in the lime-water ? 
What is the effect of this gas on flame ? 
What is the effect of it on blue litmus ? 
Why does the gas stay in the open bottle ? 
Ex. 7 4. — What if the vessel of carbon dioxide is open 
downward ? I remove the tubes 
and cork from flask c, Fig. 55, and 
then hold the flask's mouth upon the 
lip of a small wide-mouth bottle, as 
if to pour the gas, as shown in Fig. 
56. After a minute I place the flask 
upon the table and plunge the flame 
of a splinter down into the bottle, 
and afterward into the flask. The 
flame shows that the gas was actu- 
ally poured, like water, from c into the bottle. 

Ex. 75. — Is this gas soluble in water? The gas bub- 
bled through the water in a, Fig. 55, and I test that water 
to see whether there is carbon dioxide 
in it. I put some lime-water in a test- 
tube, and, after taking the rubber tubes 
from a, I lift the flask and pour water 
from it into the lime-water, as shown in 
Fig. 57. 

If the water in a has dissolved carbon 
dioxide, the lime-water will be whitened. 

Description". — Carbon dioxide is a compound of 
carbon and oxygen: this was proved by Ex. 26. We 
see that it is a colorless gas, and much heavier than air 
(Exs. 73, 74). In fact it is about one and one-half times 
heavier than air (1.529). It whitens lime-water by com- 
bining with the lime and making the white solid called 
calcium carbonate, which the water cannot dissolve, and it 




Fig. 67. 



114 COMPOSITION OF PLANTS. 

reddens blue litmus-water (Ex. 73), for a reason which will 
appear by and by. 

This gas will put out a fire (Ex. 73) just as quickly as 
will water, and for the same reason. A body will not burn 
without oxygen, and when covered with water the oxygen 
of the air cannot get to it. So when in carbon dioxide, no 
oxygen can reach the body, and the fire dies. 

So, too, this gas will cause death, just as will water. An 
animal must have oxygen to breathe, or it must die. It 
drowns in water because water keeps the air away from 
its lungs; carbon dioxide will do the same thing. There 
is too little of this gas in the open air to do harm, but 
where it collects in large quantities an animal dies because 
it can get too little oxygen to keep it alive. 

It sometimes collects in mines, and the miners call it 
choke-damp. It sometimes collects in wells, and makes 
them dangerous to enter ; a lighted candle will tell a work- 
man whether this gas is present in dangerous quantities. 
It often collects in school-rooms and churches and other 
unventilated houses, but not often enough of it to do much 
harm. The truth is that the breath of people is full of 
other gases, some of which are very poisonous, and the 
mischief in unventilated rooms is done by these compan- 
ions of the carbon dioxide instead of by this gas itself. 

Carbon dioxide is soluble in water (Ex. 75). It is found 
that water will usually dissolve about its own volume. But, 
like all gases, more will dissolve in colder water, and still 
more when under greater pressure. Nearly all water con- 
tains this gas, but the quantity in solution is generally 
small. In some springs, however, it is very abundant. It 
is so in the noted mineral springs of Saratoga. And the 
refreshing summer drink — soda-water — is nothing but 
water charged with a large quantity of this gas which has 
been forced into it by great pressure. 



COMPOSITION OF PLANTS. 115 

Carbon Monoxide. — Besides carbon dioxide there is 
another compound of carbon and oxygen called carbon 
monoxide. See p. 82. It is a colorless gas. It takes tire 
easily, and barns with a pale blue flame ; this is the flame 
which is often seen playing over the surface of a new- 
made coal-fire. When the coal burns at the bottom of 
the grate it produces carbon dioxide, as usual, but as this 
carbon dioxide goes up through the hot coal above it 
gives up a part of its oxygen and becomes carbon mon- 
oxide. And then when this monoxide comes out into hot 
air, at the surface, it takes oxygen and becomes carbon 
dioxide again. 

This gas is very likely to escape being burned. There 
may not be air enough, or there may not be heat enough 
to burn it. This should be remembered when coal is 
used for warming rooms, for carbon monoxide is a very 
poisonous gas. Accidents have many times happened 
from burning charcoal in open fires with poor draught. 
This poisonous gas escaping into the room destroys life. 

Composition of the two Oxides. — It is found by 
analysis of the two gases that the carbon monoxide con- 
tains just one-half as much oxygen as the carbon dioxide. 
The proportions are as follows : 

In carbon monoxide there are 16 of O combined with 12 of C 
" " dioxide " " 32 "'0 " " 12 « C 

What laAV does this illustrate ? 

Compounds of Carbon and Hydrogen. — ]STo other ele- 
ments form so many compounds with one another as do 
carbon and hydrogen. Of carbon and oxygen there are 
only two. Of nitrogen and oxygen there are five, and 
this is rather an unusual number for two elements only. 
But of carbon and hydrogen the compounds are many 
scores in number. They are called hydrocarbons. Just 
now we will study only one of these. 



116 COMPOSITION OF PLANTS. 

Methane. — This is the simplest one of the hydrocar- 
bons. It is commonly called marsh-gas y which is a very 
appropriate name, because it is abundant in marshy 
places. Have you never seen the water of ponds and 
quiet pools stirred by bubbles of gas breaking at the sur- 
face ? It is a very common thing to be seen in water 
standing over muddy bottoms. The bubbles are of marsh- 
gas. They are set free by the decay of vegetable sub- 
stances in the mud below. 

Marsh-gas flows from coal-beds into the mines where 
the laborers are at work. The most awful effects are 
then sometimes produced by it. It is very combustible, 
and, more than this, when mixed with air it is terribly 
explosive. Fancy it flowing into a mine, mixing with the 
air around the miners, and the mixture then touching 
the flame of the miner's lamp! The lamps and the lives 
of the miners are then extinguished at once by a terrible 
explosion. 

The miners have given this gas the name of fire-damp. 

It is found by analysis that methane is made of carbon 
and hydrogen only, and in quantities by weight which are 
as 12 to 4. 

In methane there are 12 parts of C combined with 4 parts of H. 

How many combining weights of carbon in the 12 of C ? 
How many combining weights of hydrogen in the 4 of 
H? 



ELEMEXTS, MOEECUEES, ANT> ATOMS. 

The Number of the Elements. — We have already 
seen, p. 24, that an element is a substance which has never 
yet been decomposed. 

At present (July, 1886) seventy-one elements are known. 
Some of these have been discovered very lately, and per- 
haps others may be found in the future. On the other 
hand some so-called elements have been found to be com- 
pounds, and it may be that some of the seventy-one shall 
yet be decomposed. All that we can say is that there are 
seventy-one kinds of matter which chemists to-day are not 
able, by any means in their power, to break into simpler 
bodies. As out of twenty-six letters of the alphabet all 
the words in the English language are made, so out of 
these seventy-one elements all the compounds in nature 
are formed. 

But only a few of this small number are at all abundant. 
In fact, the larger part of the earth, and all it contains, is 
made up of only about a dozen elements. All the water on 
the globe consists of oxygen and hydrogen. Four-fifths of 
the air is nitrogen. These three, with carbon, make up by 
far the larger part of all plants, and the bodies of animals. 
And as for rocks and soils, they consist chiefly of those 
just named, with eight others, — sulphur, silicon, potas- 
sium, sodium, calcium, magnesium, aluminum, and iron. 
With these exceptions, the elements are not common, and 
one-third of the whole number are very rare. 

The names of all the elements now known are given in 
the following table. The symbols and atomic weights 
will be explained soon. 

117 



118 



ELEMENTS, MOLECULES, AND ATOMS. 



THE SEVENTY-ONK ELEMENTS. 



Names. 



Aluminum . 
Antimony . 
Arsenic . . 
Barium . . 
Beryllium (*) 
Bismuth . . 
Boron . . 
Bromine . . 
Cadmium . 
Caesium . . 
Calcium . . 
Carbon . . 
Cerium . . 
Chlorine . . 
Chromium . 
Cobalt . . 
Columbium ( 2 ) 
Copper . . 
Decipium . 
Didymium ( 3 ) 
Erbium . . 
Fluorine . . 
Gallium . . 
Germanium. 
Gold . . . 
Hydrogen . 
Indium . . 
Iodine . . 
Iridium . . 
Iron . . . 
Lanthanum 
Lead . . . 
Lithium . . 
Magnesium . 
Manganese . 
Mercury . . 



Symbols. 

~A1. 

8b. 

As. 

Ba. 

Be. 

Bi. 

B. 

Br. 

Cd. 

Cs. 

Ca. 

C. 

Ce. 

CI. 

Cr. 

Co. 

Cb. 

Cu. 

Dp. 

Di. 

Er. 

F. 

Ga. 

Gr 

Au. 

H. 

In. 

I. 

Ir. 

Ee. 

La. 

Pb. 

Li. 

Mg. 

Mn. 

Hg. 



Atomic 
Weights. 

~~2L3~ 
120. 

75. 

137. 

9. 

208. 

11. 

80. 
112. 
133. 

40. 

12. 
141. 

35.5 

52. 

59. 

94. 

63.3 

142.3 

106. 

19. 

69. 

72.75? 
196.5 

1. 
113.6 
127. 
193. 

56. 
138.2 
207. 
7. 

24. 

55. 
200. 



Names. 

Molybdenum 

Nickel 

Nitrogen . 

Osmium . 

Oxygen . 

Palladium 

Phosphorus 

Platinum 

Potassium 

Rhodium 

Rubidium 

Ruthenium 

Samarium 

Scandium 

Selenium 

Silicon . 

Silver . . 

Sodium . 

Strontium 

Sulphur . 

Tantalum 

Tellurium 

Terbium . 

Thallium 

Thorium . 

Thulium . 

Tin . . 

Titanium 

Tungsten ( 4 ) 

Uranium . 

Vanadium 

Ytterbium 

Yttrium . 

Zinc . . 

Zirconium 





Atomic 


Symbols. 


Weights. 


Mo. 


96. 


Ni. 


58. 


N. 


14. 


Os. 


198.6 


O. 


16. 


Pd. 


106. 


P. 


31. 


Pt. 


195. 


K. 


39.1 


Rh. 


104. 


Rb. 


85.5 


Ru. 


103.5 


Sm. 


150. 


Sc. 


44. 


Se. 


79. 


Si. 


28. 


Ag. 


108. 


Na. 


23. 


Sr. 


87.5 


S. 


32. 


Ta. 


182. 


Te. 


125 


Tb. 


? 


Tl. 


204. 


Th. 


232. 


Tm. 


? 


Sn. 


118. 


Ti. 


48. 


AY. 


184. 


U. 


240. 


V. 


51.2 


Yb. 


173. 


Yt. 


89. 


Zn. 


05. 


Zr. 


90. 



(!) Beryllium is also called Glucinum, with the symbol Gl. 

( 2 ) Columbium is also called Niobium, with the symbol Nb. 

( 3 ) The announcement has come from Vienna that Didymium has been decom- 
posed. See Chemical News, vol. 5'2, and Nature, vol. 3'2, p. 435. 

( 4 ) Tungsten has also been called AVolframium. 



ELEMENTS, MOLECULES, AND ATOMS, 119 

The Three Forms of Matter. — Earth, water, and air 
represent the solid, liquid, and gaseous forms of matter. 
So far as we know, all kinds of matter are in one or another 
of these three conditions. But ice and water and steam 
are all one kind of matter, and yet one is a solid, another 
is a liquid, and another a gas. 

Ice, when heated, melts into water, and water when 
heated to a higher temperature boils into steam. We 
find that many other solids are like ice in this respect — 
they melt when heated, and that other liquids are like 
water — they may be changed into vapor by heat. 

These are facts. We know them to be so, because we 
have seen these changes happen over and over again. 
Indeed, so many substances have been tried and found to 
be solid at low temperature, liquid at some higher tempera- 
ture, and gaseous at some temperature higher still, that 
we feel quite sure that the facts are the same for all ; and 
so we say that 

The solid, liquid, and gaseous forms of matter depend on 
the amount of heat in them. 

This one statement, made out of many facts, is a law. 

Another Effect of Heat. — If we warm a piece of 
iron it will become larger, and if we cool it it will become 
smaller. The same thing is true of a piece of wood; it is 
larger when it is hot than when it is cold. A given weight 
of water, or of air, is found to be larger and larger as it is 
heated more and more. These are facts. They have been 
proved to be true of the substances named, and of a great 
many more beside. Now let us put all such facts together 
into one statement by saying that 

Heat makes a body larger without changing its iveight. 

This is a law. A law, in science, is simply a single 
statement which covers a large number of facts. 



120 ELEMENTS, MOLECULES, AND ATOMS. 

The Reason. — A body is larger when it is hot; can 
we tell why it is so ? Nobody knows with absolute cer- 
tainty why bodies should expand when heated. But the 
best way to account for it is to suppose that matter is 
made up of very small particles which are quite separate 
from one another, so that they may be driven farther apart 
or crowded nearer together. Heat drives them farther 
apart and makes them fill more space, and cold allows 
them to fall more closely together, and thus to fill a smaller 
space. Surely this is a very good reason why heat should 
make a body larger, and cold should make it smaller. If a 
body were made up of separate particles it would behave 
just as we see that it does behave when heated and cooled, 
and so we may suppose that it is made up of such particles. 
Perhaps it is so. 

If we imagine every body to be made up of small parti- 
cles which are quite separate, we can understand many 
other facts beside expansion by heat. Take, for example, 
the fact that you make an india-rubber ball smaller 
when you squeeze it. If we are right in supposing that 
the ball is made up of a great multitude of small, separate 
particles, the hand would make it smaller by crowding 
them closer together. The ball acts just as if it were made 
up of separate particles. Probably it is so. 

In a great many other ways bodies behave exactly as if 
they were made up of such separate particles. Indeed, so 
far as they have been examined, the facts are always just 
what we should expect if matter be made up of small par- 
ticles which are some distance apart. On this account we 
believe it to be so. 

Now, something which is believed because it gives good 
reasons for a large number of facts is called a theory. 
That all bodies are made up of minute particles which do 
.not touch one another is our theory of matter. 



ELEMENTS, MOLECULES, AND ATOMS. 121 

The student cannot too early nor too carefully fix in his 
mind the difference between facts and theories. Facts are 
things known to be true ; theories are things believed to be 
true. 

Molecules. — According to the theory of matter just 
stated, all bodies are made up of separate particles. These 
particles cannot be seen. They are so small as to be 
quite beyond our sight with the best microscope. They 
are the very smallest pieces of a substance which can pos- 
sibly exist, so that to divide them into parts will change 
the substance into something else. They are called mole- 
cules. A molecule is a particle of substance so small that 
it cannot be divided without changing the nature of the 
substance. Molecules of the same substance are all alike, 
but the molecules of different kinds of matter are not alike. 

Some Facts about the Expansion of Gases. — It has 
been found by very careful and repeated experiments that 
if we take 273 cc. of air as cold as freezing water, 0° C. 
and warm it just 1° C, it will become just 274 cc. Add 
another degree of heat and it will "become 275 cc, and so 
on, each degree of heat expanding it just 1 cc. In other 
words, one degree of heat will always expand air just 
2-I-3 of what its volume is at 0° C. 

The rate has been found also for many other gases, and 
it is the same for all. This is a very important fact. It 
is not so among solids and liquids ; no two solids expand 
exactly alike ; no two liquids. Why do all gases expand 
alike when heated, while solids and liquids do not ? 

Again, if air is pressed in a close vessel it will be 
crowded into smaller volume ; but, on the other hand, if 
we put less pressure on it the air will expand. Other 
gases behave in the same way. And the same change of 
pressure will change the volume of one just exactly as 
much as another. This is another important fact. It is 



122 ELEMENTS, MOLECULES, AND ATOMS. 

not a fact for solids and liquids ? Why should the same 
pressure condense all gases exactly alike ; and the removal 
of the same pressure expand all gases exactly alike ? 

The Theory. — These and other facts led Avogadro, in 
1811, to suppose that when two gases are equally warm, 
and under the same pressure, a cubic inch of one contains 
just as many molecules as a cubic inch of the other. And 
since all gases behave, in so many respects, just as they 
would be expected to do if this famous hypothesis were 
true, it is believed to be as Avogadro supposed. 

Equal volumes of all gases, at the same temperature and 
pressure , contain the same number of molecules. 

This is Avogadro's theory : but it is often called Avo- 
gadro's law. 

Chemical Changes are Changes in the Molecules.— 
When water is decomposed by electricity (Ex. 37) it is 
broken into two parts ; one part is hydrogen, the other is 
oxygen. The change is believed to take place in each sep- 
arate molecule. When mercuric oxide is heated (Ex. 5) 
every molecule of it is broken into two parts ; one is mer- 
cury, the other oxygen. When marble and hydrochloric 
acid act (Ex. 73) every molecule of these two substances 
is broken into two parts, and then those parts fall together 
again, in a different way, and make the molecules of two 
new kinds of matter. 

Atoms Now what shall we call the smaller particles 

in a molecule ? They are atoms. These are the very 
smallest pieces of matter that take part in a chemical 
change. They cannot be divided by any known process 
whatever. All bodies are made up of molecules, and mole- 
cules are made up of atoms. 

If the atoms of a molecule are alike, the substance is 
an element, but if the atoms in a molecule are not all alike 
the substance is a compound. 



ELEMENTS, MOLECULES, AND ATOMS. 123 

The Explanation of the Law of Multiple Propor- 
tions. — The law of multiple proportions is the statement 
of a fact. We know that the combining weight of an ele- 
ment is never divided in chemical changes ; can we tell why ? 

The most natural reason is found by supposing the 
combining weight to be the weight of a particle of mat- 
ter which cannot be divided, that is, of an atom. Such 
particles will pass unbroken from one kind of compound 
into another. One of them may go alone, or some whole 
number of them may go together. The weight of one of 
them is the combining weight of the element, and of any 
whole number of them, is a multiple of that combining 
weight. And so — 

If one element combines with another, in more pro- 
portions than one, these proportions must be multiples of 
its combining weight. 

The Atomic Theory. — This theory of matter is known 
as the Atomic Theory. Its main points are these : All 
bodies are made up of molecules, and molecules are made 
up of atoms. All chemical changes are changes in the 
arrangements of the atoms, and the combining weights 
of the elements are the relative weights of their atoms. 

The theory of atoms was first proposed in 1808 by John 
Dalton. He was the first to see clearly that the combi- 
nation of the elements, in definite and in multiple pro- 
portions, are facts which seem to show that there are 
particles of matter which cannot be divided. The atomic 
theory was made to explain these laws of combination, and 
it is well fixed in chemistry, because it not only explains 
these, but has been found to explain new facts, as fast as 
they have been discovered, down to the present time. 

Symbols of Elements. — Instead of writing the full 
name of the element hydrogen, we may simply write 
the first letter, H, to represent it. H is then called the 



124 ELEMENTS, MOLECULES, AND ATOMS. 

symbol of hydrogen. In the same way is the symbol of 
oxygen, X of nitrogen, and C of carbon. 

Sometimes the names of two or more elements begin 
with the same letter, as carbon, calcium, and copper. In 
this case a small letter is used with the large initial, thus : 
the symbol of calcium is Ca, and that of copper is Cu. 
The latter is from the Latin name of copper, which is 
Cuprum. A symbol represents the name, and also just 
one atom of an element. 

Formulas of Compounds. — Instead of writing the full 
name mercuric oxide, we may simply write the symbols 
of the elements of this compound, side by side, Hg for 
mercury and for oxygen, making HgO to represent it. 
HgO is then called the formula for mercuric oxide. H CI 
is the formula for hydrochloric acid. 

The formula of a compound represents one molecule of it. 

H 2 is the formula for water ; the small figure 2 means 
that there are two atoms of hydrogen combined with one 
of oxygen in the molecule. C 2 is the formula for carbon 
dioxide, and shows that one molecule contains one atom 
of carbon and two atoms of oxygen. H 2 S 4 is the formula 
for sulphuric acid ; what does it show ? 3 H 2 S 4 means 
three molecules of sulphuric acid, and 2H 2 means two 
molecules of water. Notice the different meaning of 
figures placed before the formulas and those placed at the 
right and a little below the symbols, in the formula. 

In reading symbols and formulas, the names of the sub- 
stances, and not the letters used, should always be given. 
We should use symbols and formulas to shorten writing, 
but not to shorten speech. 

Atomic Weights. — We have learned that hydrochloric 
acid contains 35.5 times as much chlorine as hydrogen ; we 
may say this of any quantity ; it is true of one molecule, 
which contains one atom of chlorine and one of hydrogen. 



ELEMENTS, MOLECULES, AND ATOMS. 125 

These numbers, 1 and 35.5, are called the atomic weights 
of hydrogen and chlorine, because they are supposed to 
represent the relative weights of the atoms of these two 
elements. We have no idea how much, or rather how 
little, the atom of hydrogen really weighs, but we do be- 
lieve that, whatever it does weigh, the atom of chlorine 
weighs 35.5 times as much. We cannot tell the weight 
of either, in fractions of a gram or ounce, but we can call 
the weight of the hydrogen atom 1, without saying what, 
and then we can say that an atom of chlorine weighs 35.5. 

These numbers are the same as those which have been 
called combining weights, p. 98. We know that they are the 
smallest relative weights of these elements which combine ; 
this is a fact discovered by experiment. It is believed that 
they represent the weights of the atoms of these elements. 
This is a part of the atomic theory. 

And now we see that the symbol of an element not 
only represents one atom, but also one atomic weight. 

Molecular Weights. — If a molecule is made of atoms 
we can find its weight by adding the weights of its atoms 
together. There are three atoms in a molecule of water, 
H 2 0, two of hydrogen and one of oxygen. The weight 
of an atom of hydrogen is 1, and of an atom of oxygen 
is 16, and the weight of all three atoms together must be 
18. The molecular weight of water, H 2 0, is therefore 18. 
It is not 18 grams, nor 18 grains, but simply 18 times as 
much as the iveight of an atom of hydrogen. 

The atomic weights are given in the table on p. 118, and 
these will enable one to find the molecular weight of any 
substance whose formula is known. Try it in the follow- 
ing examples. 

AVhat is the molecular weight of hydrochloric acid, H CI ? 

" sodium chloride, XaCl? 

" " " " mercuric oxide, Hg O ? 

" " " " sulphuric acid, H 2 S0 4 ? 



126 ELEMENTS, MOLECULES, AND ATOMS. 

Reactions. — Chemical changes are also called reactions. 
Now chemical changes are changes in the molecules of sub- 
stances, and we can show what they are by making changes 
in the formulas which represent the molecules. In this 
way symbols and formulas are a great help in the study 
of experiments. 

For example, suppose we wish to know all about the 
reaction of sodium and hydrochloric acid. We must 
begin by making the experiment. We may then study 
the results by the help of symbols and formulas. 

Reaction of Sodium and Hydrochloric Acid. Ex. 
76. — I measure 2 cc. of strong hydrochloric acid into a 
test-tube which stands in the rack, drop in upon it a piece 
of sodium as large as a small pea, and loosely cover the 
mouth of the tube with a piece of paper. After half a 
minute, I push the flame of a lighted match down into 
the tube. When the sodium has disappeared, I drop in 
another piece of about the same size. 

What gas is set free by the chemical action ? 

What proof is seen that another substance is produced ? 

To find out what is this second product, I first let it 
settle to the bottom of the tube, and then pour off the 
liquid so carefully that I leave the solid behind almost dry. 
In this way I get rid of most of the acid which was not 
decomposed. I then add three or four cubic centimeters 
of water, to dissolve the white solid, pour the solution 
into a small porcelain dish, and heat it over a small flame 
until the water is all driven off and the solid remains dry 
and white. The dish must now stand until cold, after 
which I add a few drops of water in which the white solid 
again dissolves. By tasting this liquid you may learn 

What is this second product of the chemical action. 

We have now got the facts about the reaction we are 
studying. To get the facts is always the first step in an 
investigation. 



ELEMENTS, MOLECULES, AND ATOMS. 127 

Next write the Reaction. — Now that we know what 
substances were used and what new substances were made, 
the next step is to use formulas and signs to show what 
happened. 

We added sodium to the hydrochloric acid in the tube ; 
we can show that fact by writing the symbol of sodium, 
which is Na, and the formula of the acid, which is H CI, 
with the sign of addition between them, thus : Na + H CI. 
We know by the taste, and by the explosion, that common 
salt and hydrogen were produced. We can show this by 
writing the formula of common salt, or sodium chloride, 
Na CI, and the symbol of hydrogen, H, with the sign of 
addition between them, thus : NaCI + H. We know that 
there is no loss nor gain of matter in any chemical change. 
The new substances must contain every atom of the old, 
and no others. We can show this by writing the old sub- 
stances and the new, with the sign of equality between 
them. Thus we have — 

Na + H CI = Na CI + H 

We read this reaction in this way : one atom of sodium, 
with one molecule of hydrochloric acid, yield one mole- 
cule of sodium chloride, and one atom of hydrogen. This 
describes the chemical change which took place. 

Now use Atomic Weights. — This chemical expression 
may be changed into numbers by writing the atomic weight 
of each element, under its symbol, wherever that symbol 
appears. Thus — 

Na + HC1 = XaCl + H 
23 + (1 + 35.5) = (23 + 35.5) + 1 
23 + 36.5 = 58.5 + 1 

If we had to make a quantity of common salt by this 
process this last equation would be very useful because it 
tells us just how much of the substances to use. We may 






128 ELEMENTS, MOLECULES, AND ATOMS. 

call these numbers grains or grains or pounds, or any other 
weights we please. The equation shows that if we use 28 
grams of sodium and 36.5 grams of hydrochloric acid, we 
can get just 58.5 grams of salt and 1 gram of hydrogen. 
Knowing this it is easy to find how much of the constit- 
uents to take for any desired quantity whatever of the 
compound. 

Finally solve a Problem. — How much sodium would 
be needed to make 100 g. of common salt by reaction with 
hydrochloric acid ? 

If for 58.5 g. of salt we need 23 g. of sodium, then for 
100 g. of salt Ave should need J g.g x 23, which is 39.31 + . 

Another Example. — Let us study the decomposition of 
mercuric oxide by heat. We have made the experiment 
already. In Ex. 5 it was found that mercury and oxygen 
were the products. We take the symbols from the table, 
p. 118, and write the reaction thus : 

Hg O = Hg + O 

Read this equation in full. Eefer to the table of ele- 
ments, p. 118, for the atomic weights, and put them under 
the symbols. What does this new equation show ? 

How much mercury could be obtained from 100 g. of the 
oxide ? And how much oxygen ? 



ACIDS, BASES, AND SAINTS. 

Acids. — We have already made use of several substances 
called acids. We now set out to discover just what is 
meant by the term acid. Let us examine a few of these 
substances for this purpose. 

Ex. 77. — I fill a bottle two-thirds full of water and add 
enough solution of blue litmus to color it distinctly. I 
next add dilute sulphuric acid, 1 of acid to 10 of water, 
drop by drop, and note the change in color. 

I now add a drop or two of the same acid to a test-tube 
nearly full of water, and touch a drop of this dilute solution 
to my tongue, and note the taste of the acid. 

I finally pour 5 cc. of strong sulphuric acid into 40 cc. 
of water in a bottle, drop into it a clipping of sheet-zinc, 
and cover the bottle with a square of heavy paper. In a 
few moments I bring a lighted match to the mouth of the 
bottle, lifting the cover at the same time, and note the 
combustion which takes place. What is this gas which 
is set free by the metal ? 

Ex. 78. — I now use hydrochloric acid instead of sul- 
phuric, and again note the 

Change in the color of the blue litmus. 
Taste of the acid. 
Action with zinc. 

Ex. 79. — I next try acetic acid, and use magnesium 
instead of zinc, I put 10 cc. of the acid in a test-tube, and 
drop upon it a short piece of magnesium ribbon. Xote 
whether the same gas is given off as in the other cases. 
Note also the taste of the acid, and its action on blue litmus. 

129 



130 ACIDS, BASES, AND SALTS. 

Ex. 80. — I repeat the experiment with acetic acid, but 
use iron instead of magnesium. I add the iron in the form 
of filings, or the smallest tacks, and gently heat the liquid. 

Is there any gas set free ? Is it hydrogen ? 

Ex. 81. — I use acetic acid again, but this time I add 
small clippings of zinc, and heat the acid. Is the action 
the same as before ? 

We find that sulphuric acid, hydrochloric acid, and acetic 
acid are alike in three things : they are all sour to the taste, 
will redden blue litmus, and yield hydrogen by the action 
of a metal. There are many other substances having these 
same characters. All such are called acids. 

The Chief Characteristic. — The following table shows 
the composition of several acids, by formulas : 

Nitric acid HN0 3 

Sulphuric acid H 2 S 4 

Phosphoric acid H 3 P 4 

Hydrochloric acid H CI 

Hydroiodic acid HI 

Hydrobromic acid H Bl- 
and a glance at these symbols shows that hydrogen, H, is 
a constituent in every one. Every acid contains hydrogen. 

But there are many compounds containing hydrogen 
which are not acids. An acid is a compound containing 
hydrogen, which may be driven out by a metal, as in our 
experiments. This is the chief character of an acid. 

The two Classes. — Look at the two sets of formulas 
in the table. In each acid of the first set, oxygen, 0, is 
present ; it is not to be found in those of the second. 

Now we may learn from this that there are two classes 
of acids. One class contains the element oxygen, the other 
does not. 



ACIDS, BASES, AND SALTS. 131 

Salts. — When in Ex. 77 our zinc drove the hydrogen 
out of sulphuric acid, zinc sulphate was also made. 
If we write the reaction — 

Zn + H 2 S0 4 =:H 2 + ZnS0 4 

it shows how zinc and sulphuric acid may yield hydrogen 
and zinc sulphate. 

We see that 1 atom of the metal, Zn, takes the 'place of 
2 atoms of hydrogen, H 2 , in the molecule of acid, so that 
instead of H 2 S 4 we have Zn S 4 . 

We should be careful to notice that the metal puts itself 
in the place of the hydrogen of the acid to form the new 
molecule. 

The action is the same when zinc acts on other acids 
instead of sulphuric. The zinc drives hydrogen out and 
puts itself in the place of it. 

Many other metals have the same power to act upon 
acids. Not every metal can do this to every acid (Ex. 81), 
but the power to put itself in the place of hydrogen in 
acids is very common among the metals. 

The new compounds, formed by this action of the metals, 
are called salts. When sodium and hydrochloric acid are 
used, the new compound, as we have seen, is common salt ; 
you have only to evaporate the liquid to get the familiar 
white solid. Every acid would yield a different kind of 
salt with sodium. Each different metal also yields a 
different salt with every acid on which it acts. 

Definition. — A salt is a compound formed by putting a 
metal in the place of hydrogen in an acid. 

Hydroxides. — Some metals act on water very much 
as the metals act on acids, but the new compounds will be 
of a quite different character. Thus : 

Ex. 82. — \ fill a bottle half full of water; add just 
enough litmus to color it distinctly ; change its color to red 



132 ACIDS, BASES, AND SALTS. 

by stirring it with a rod moistened with an acid, and then 
drop upon its surface a bit of sodium. Xote the change 
in color, and prove that hydrogen is set free. 

Ex. 83. — I repeat the experiment, but use 25 cc. of 
water without the litmus. When the sodium is gone, I 
examine the liquid in three ways: 

1. I moisten the end of a rod with the liquid, touch my 
tongue with it, and note the taste. 

2. I try its action on blue litmus-water. I then try it on 
red litmus-water in this way: I take a little water in a 
tube, blue it with litmus, and then redden it with a rod 
moistened with acid. To this I add a few drops of the 
liquid, and note the change in color. 

3. I put the rest of the liquid in a porcelain dish and 
evaporate it to dryness, using a small flame toward the 
end of the operation, and note the appearance of the solid 
left behind. 

The Facts. — The sodium decomposes the water, and 
the two new substances are hydrogen gas, and a white 
solid which is very " alkaline " to the taste, and able to 
restore the blue color to reddened litmus. 

We may write the reaction in the usual way : 

Na + H 2 = NaHO + H 

Sodium Water Sodium hydroxide Hydrogen 

and this shows that 1 atom of the metal, Xa, takes the 
place of 1 atom of the hydrogen, H ? in the molecule of 
water, and makes a new molecule of what is called sodium 
hydroxide, NaHO. This sodium hydroxide is the white 
substance left behind in the dish. 

It is named for the elements in it — sodium, hydro- 
gen, and oxygen. The last two names are combined in 
hydroxide, and so we get the name sodium hydroxide. 

In like manner we have potassium hydroxide, K H 0, 
and ammonium hydroxide, Am HO. 



ACIDS, BASES, AX J) SALTS. 133 

Ex. 84. — I half till two bottles with litmus-water red- 
dened by acid, and then to one I add drops of potassium 
hydroxide (caustic potash) solution to the other drops of 
ammonium hydroxide (ammonia). 

Note the change in the color of each. 

Carefully learn the taste of each. 

The Facts. — These three hydroxides are alike, very 
alkaline in taste, and alike able to restore the blue of red- 
dened litmus. They restore the blue color by decomposing 
the acid which reddened it. In this way they neutralize 
the acids. This is their chief characteristic. 

It has been found by experiment, that nearly all metals 
have compounds of this kind. The hydroxides are a very 
large class indeed. 

Definition. — A hydroxide is a compound of a metal 
with hydrogen and oxygen, which will neutralize an acid. 

Other Names. — These substances are also called hy- 
drates ; instead of sodium hydroxide we may say sodium 
hydrate. They are also called bases. 

Reaction of Bases and Acids. — But how does a base 
or hydroxide neutralize an acid ? Take the sodium hy- 
droxide and hydrochloric acid for example. 

Ex. 85. — I put 15 cc of hydrochloric acid into a bottle 
and drop into it a small bit of litmus-paper, 1 which in- 
stantly becomes red. I next add a solution of sodium 
hydroxide little by little, shaking or stirring the liquid 
well after each addition. I watch the color of the litmus- 
paper : it will after a while show signs of turning blue. 
I then add the hydroxide, a drop at a time, until after the 
last drop the paper remains blue. By this sign I know 
that the acid is neutralized. 

1 Litmus-paper is made by soaking filter-paper in a strong solu- 
tion of litmus in water and then drying it; the paper has a deep blue 
color. 



134 ACIDS, BASES, AND SALTS. 

I next search for the product of the action. I put the 
liquid into a porcelain dish and evaporate it down care- 
fully until dry. Let it cool, and then examine the residue. 
]Sote its color and its taste. By its taste we know what 
this new substance is. 

We find that common salt (Na CI) is one product of the 
action of these two liquids. By writing the reaction, we 
may discover that there should be another. For we must 
have new substances enough to contain all the atoms in the 
old ones. Thus, if we write — 

HC1 + XaHO = NaCl + HHOorH 2 
acid base salt water 

we see that water must be a product of the action. In 
this case the acid and the base neutralize each other by 
forming a salt and water. 

In other cases the action is the same. It is a fact that 
when an acid and a base act upon each other the result is 
to produce a salt and water. There are few exceptions 
(p. 95) to these important facts, viz. : 

When a metal acts on an acid a salt and hydrogen are 
produced. When a base acts on an acid a salt and water 
are produced. 

Neutral Compounds — Water is a good example of 
bodies which are neither acids nor bases nor salts. It 
will not change the color of litmus either to red or blue. 
It is not sour to the taste like the acids, nor caustic like 
the bases, nor is it made by putting a metal in the place 
of hydrogen in the acids, as the salts are. There are a 
great many other compounds like water in these respects. 
Bodies which will not change the color of either blue or red 
litmus are called neutral bodies. 



ACIDS, BASES, AND SALTS. 135 



CHEMICAL NAMES. 

The names of chemical compounds are not invented 
to simply suit the fancy of the chemist ; they are made 
by certain rules, and are meant to show the composition of 
the substances to ivhich they are given. 

The Names of Acids. — Sulphuric acid is made up of 
sulphur, oxygen, and hydrogen; its name is so made that 
the presence of these three things is shown. 

The presence of sulphur is shown by using the name 
of that element. The presence of oxygen is shown by 
the ending ic. The presence of hydrogen is shown by the 
word acid, because all acids are known to contain this 
element. 

Sulphurous acid is another compound of these same 
elements, sulphur, oxygen, and hydrogen. Sulphur is 
shown by its own name as before. Oxygen is shown by 
the ending ous. Hydrogen is shown by' the word acid as 
before. 

It will be seen that sulphuric acid and sulphurous acid 
are made of the same elements. The first contains a larger 
proportion of oxygen than the other, and this is their only 
difference in composition. Now ic is used in the name of 
the one that contains the larger proportion of oxygen, and 
ous in the name of the other. 

In the same way we have two acids of phosphorus : 
they are called phosphor^ acid and phosphorus acid. The 
first contains a larger proportion of oxygen than the last. 
This fact is shown by using the ending ic in the name of 
the first, and ous in the name of the last. 

In some cases more than two acids are made of the same 
elements. Prefixes are then used in addition to the end- 
ings ic and ous. These prefixes are hypo and per. There 
is, for example, the hyposulphurous acid. It contains a 



136 ACIDS, BASES, AND SALTS. 

less proportion of oxygen than the sulphurous acid, and 
this is shown by the prefix hypo. The prefix per means 
a larger proportion of oxygen. There is, for example, 
the perchloric acid. It contains a larger proportion of 
oxygen than the chloric acid: this is shown by the pre- 
fix per. 

The Names of Salts. — The name of a salt is intended 
to show the names, of the metal and the acid, by which the 
salt is supposed to be made. If sodium act on sulphuric 
acid, hydrogen is liberated and a salt is at the same time 
formed ; this salt is called sodium sulphate. It is easy to 
see that this name suggests the name of the acid and also 
of the metal. When sulphuric acid is used the salt which 
is made is called a sulphate, no matter what metal is 
employed. 

But " sulphurous acid yields a class of salts which are 
called sulphites. Notice the difference: 

Sulphuric acid yields sulphates. 
Sulphurous acid yields sulphites. 

The same difference is found in other cases. A salt 
formed by chloric acid is called a chlorate; but one formed 
by chlorous acid is called a chlorite. Nitric acid yields 
nitrates, but nitrous acid yields nitrites. 

The rule is this: if the name of the acid ends in ic, 
the names of its salts shall end in ate; but if the name 
of the acid ends in oris, the names of its salts shall end 
in ite. 

The Names of Bases. — All bases are made up of 
hydrogen, oxygen, and a metal, and their names show this 
fact. The word hydroxide suggests hydrogen and oxygen, 
and hydroxide is the name of this whole family of com- 
pounds. Each individual member of this family is dis- 
tinguished by the name of the metal which is in it. 



ACIDS, BASKS, AND SALTS. 137 

The following examples will make this method clear. 
See how the names of the elements suggest the name of 
the base which they form, and how the name of the base 
also suggests the names of the elements of which it is 
made. 



■ l oo 



Sodium, hydrogen, oxygen, form the Sodium hydroxide. 
Potassium, " " " " Potassium hydroxide. 

Calcium, " " " " Calcium hydroxide. 

Iron, " " " " Ferric hydroxide. 

Iron, " " " " Ferrous hydroxide. 

There are in rnairy cases two hydroxides of the same 
metal, and the endings ic and ous are used to distinguish 
them. The names of the iron hydroxides illustrate this : 

Ferric hydroxide ....... Fe 2 (H 0) 6 

Ferrous hydroxide Fe (H 0) 2 



CHLORINE AND THE CHLORIDES. 



More than a hundred }^ears ago — it was in 1774 — the 
Swedish chemist Scheele was studying the action of hy- 
drochloric acid on a black powder known as the " black 
oxide of manganese." To his surprise a heavy greenish 
gas was produced. Sir Humphry Davy afterward called 
this gas chlorine. 

Chlorine is a very suffocating substance, and in all experi- 
ments with it we must be careful to not breathe it. When 
we make the gas, and when we use it, there must be the 
utmost care to have our apparatus air-tight, and to prevent 
the escape of this noxious gas. 

The following arrangement of our gas-making apparatus 
will enable chlorine to show several of its properties with- 
out escaping to poison the atmosphere of the room. 

Preparation of Chlorine. — We will adopt the original 
method, and make the gas by the action of "black oxide 

of manganese" 
on hydrochloric 
acid. 

Ex. 86. — In- 
to a I put 50 cc. 
water, and close 
the flask tightly 
with its stop- 
per. By means 
of a piece of 
small wire I 
Fig - 58, hang a strip of 

moist blue litmus-paper to the stopper of b, and press it 

down into the flask. 

138 




CHLORINE AND THE CHLORIDES. 139 

I fix a piece of " gold leaf " (Dutch metal) in the same 
way, and enclose it in c. I fill the bulb of a drying-tube 
loosely with cotton, and then fill the wide part of the 
tube with dry slaked lime and cork it tightly. 

I then join all these parts, as shown in the cut, by means 
of rubber tubing, — the side-neck with the long glass tube 
of a, the short tube of a with the long tube of b, the 
short tube of b with the long tube of e, and the short tube 
of c with that of the drying-tube, the small end of which 
I place in a bottle, d. 

Finally, to make the chlorine I put 25 g. of manganese 
dioxide, Mn0 2 , into the side-neck flask, pour in upon it 
100 cc. strong hydrochloric acid, press home the solid 
rubber stopper, and apply a small flame of the Bunsen. 
The heat must be gentle. The chlorine will slowly drive 
the air over from flask to flask, and out at d; but if the 
joints are as tight as they may be, no chlorine will escape 
into the room. 

The chlorine soon fills the side-neck flask, as may be 
seen by its color, and then bubbles through the water in 
a, and passes slowly on toward d. 

What is the action of €1 and H 2 0, shown in flask a ? 
What is the effect of CI on the color of litmus, shown in bf 
What is the effect of CI on Dutch metal, shown in c ? 
Why are there no bubbles of CI in the bottle d ? 

The Facts. — The chlorine comes from the hydrochloric 
acid. The reaction may be written as follows : 

Mn0 2 + 4HC1 = MnCl 2 -f 2H 2 0+2C1 

Manganese dioxide Hydrochloric acid Manganese chloride Water Chlorine 

Chlorine is a greenish-yellow gas, whose odor is pungent, 
and suffocating in the highest degree. Cold water dis- 
solves about two and one-half times its own bulk of chlo- 
rine, and then has the same color as the gas itself. This 



140 CHLORINE AND THE CHLORIDES. 

chlorine-water may be used instead of the gas for many 
purposes ; it will cause the same chemical actions. We see 
also (flask b) that chlorine destroys the color of litmus, 
and (flask c) that it combines with " gold leaf/' and that 
it is greedily absorbed by the lime in the " drying-tube." 

The actions of chlorine on colors and on the metals are 
important. Let us study them further. 

Bleaching Chlorine destroys the color of litmus (b). 

Will it also bleach other colors ? 

Ex. 87. — I fill a test-tube half-full of water, and color 
it with black writing-ink. I slip the rubber tubes off 
from the glass tubes of flask a, and then, carefully invert- 
ing the flask over the mouth of the test-tube, as in Fig. 57 
I let a few drops of chlorine-water run into the black liquid. 

Ex. 88. — I use cochineal, or an aniline dye, or the petal 
of a flower, or a piece of calico cloth, instead of the inky 
water in the last experiment. 

Ex. 89. — I take a piece of paper covered with writing in 
red ink, and a piece of newspaper covered with printing, 
and moisten both with the chlorine-water. 

Is the color discharged in both cases ? 

What is the coloring matter of printers' ink ? 

The Facts. — This power of chlorine to destroy color- 
ing matters is made use of on a large scale in the art of 
bleaching. All colors which are made from vegetable or 
animal substances will be removed by chlorine in the 
presence of ivater : dry chlorine does not bleach. Nor are 
mineral colors (carbon of printers 7 ink) disturbed by it. 
The bleaching of linen and cotton goods and paper is done 
by the use of chlorine. 

Chlorine also destroys bad odors, and it is much used in 
hospitals and elsewhere for this purpose. It is the most 
powerful disinfectant. 



CHLORINE AND THE CHLORIDES. 141 

Chlorine destroys colors and odors, by taking hydrogen 
away from them. In some cases the color or the odor 
gives np its hydrogen directly to the chlorine, bnt in 
others it is water which gives up its hydrogen to the 
chlorine, and then the oxygen which is set free attacks 
the substance of the color or the odor and decomposes it. 

Bleaching Powder. — Chlorine is absorbed quite greedily 
by slaked lime. The product is called bleaching powder, and 
this, instead of chlorine-water, or the gas itself, is used in 
the arts. 

Ex. 90. — I remove a part of the lime from the drying- 
tube, Ex. 86, to a dish and cover it with water. After 
stirring it well, I pour it on a filter, and catch the filtrate 
in a test-tube. I then add a little of this clear solution to 
some inky water or litmus solution in another tube. 

By passing chlorine-gas over dry lime in large chambers, 
instead of in a tube, immense quantities of this powder 
are made, to be used as a bleaching agent and disinfectant. 

The Chlorides. — Chlorine readily combines with the 
metals and changes them into chlorides. This action took 
place in flask c (Ex. 86). The leaf of "Dutch metal" is 
said to be made of zinc and copper, and if so, the white 
residue is made up of zinc chloride and copper chloride. 
Let us search for the copper chloride. 

But we should first examine some copper chloride itself, 
so that we may be able to identify it. 

Ex. 91. — I put a little of a known specimen of copper 
chloride into a test-tube and acid a little water. It easily 
dissolves. 

What is the color of the strong solution ? 
What is the color if more and more water be added ? 
What happens if a piece of clean iron is left in the 
solution ? 



142 CHLORINE AND THE CHLORIDES. 

I next add to some solution in another tube a little 
ammonia, and then add more, and more, until the blue 
precipitate made at first is dissolved to a clear, fine blue 
liquid. 

A compound of copper may be known by the green or 
blue color of its solution, by the metallic copper set free by 
iron, and by the action of ammonia. 

Ex. 92. — I now carefully take the stopper and tubes 
from the flask c ; the white residue of the metal is lifted 
out with them. I carefully wash this residue into a porce- 
lain dish with as little water as will remove it. I look for 
the color, and if I find none I evaporate the solution down 
to a small bulk. Finally, I insert a bright clean needle or 
knife-blade and leave it a few minutes. 

Compare these results with those in Ex. 91, and decide 
whether the chlorine produced copper chloride in the 
flask c, in Ex. 86. 

Chlorides by Chlorine Water. — Metals are changed 
to chlorides, not only by chlorine gas, but also by chlorine 
water. Thus : 

Ex. 98. — I put a leaf of "Dutch metal/' about two square 
inches, into a test-tube and pour upon it 5 cc. chlorine-water 
from a, and shake it until dissolved. I then carefully 
slide a clean iron nail down into the solution. 

Does the color of the solution indicate a copper com- 
pound ? Does the action of the iron prove its presence ? 

After half an hour take out the iron, and put in a fresh 
bright piece. If the action is over no copper will now be 
deposited. Keep this liquid for Ex. 97. 

Chlorides by Hydrochloric Acid. — But the most 
usual way of changing metals to chlorides is by means of 
hydrochloric acid. Thus : 

Ex. 9Jf. — Into 5 cc. strong hydrochloric acid I put several 



CHLORINE AND THE CHLORIDES. 143 

small bits of iron, such as small tacks. Hydrogen escapes 
with effervescence. I let the tube stand until the action is 
over. 

Note the color of the iron chloride now in solution. 

Get the solid chloride out, by evaporating the liquid. 

The reaction may be written in this way : 

Fe + 2HC1 = FeCl 2 + 2H 

Iron Acid Ferrous chloride Hydrogen 

which shows that an atom of iron, Fe, takes the place 
of two atoms of hydrogen in the acid, and makes a new 
molecule of ferrous chloride, setting two atoms of hydro- 
gen free. Thus the iron is changed into a chloride. 

Iron has a stronger attraction for chlorine than hydrogen 
has, and can take the chlorine away from the hydrogen in 
the acid. This is also true of many other metals beside 
iron. 

Chlorides by Aqua Regia. — When strong hydrochloric 
acid is mixed with nitric acid, they decompose each 
other; chlorine is set free, but stays in the solution. 
Xow this mixture will do what neither of the acids sepa- 
rately can do : it will dissolve gold and platinum, changing 
them into chlorides. Gold has been called the king of 
metals, and this liquid which dissolves it is called aqua 
regia, the meaning of which is " royal water." Aqua regia 
is the most powerful of all agents for changing metals into 
their chlorides. For example : 

Ex. 95. — I put 2 cc. strong hydrochloric acid into a test- 
tube and add about one-fourth as much strong nitric acid. 
Into this I drop two or three small " tacks." Chemical 
action is evident at once, and the iron slowly wastes away. 
The liquid changes color as the iron chloride increases, 
and toward the end orange vapors of a suffocating odor 
may appear. Keep this liquid. 



1-44 CHLORINE AND THE CHLORIDES. 

Two Chlorides of one Metal. — The color of the liquid 
containing the iron chloride made by aqua regia is quite 
different from that of the iron chloride made by hydro- 
chloric acid. Let us try to find the reason. 

Ex. 96. — I repeat the experiment with hydrochloric 
acid (Ex. 94), and when the action is over compare the 
liquid with that made by aqua regia in Ex. 95. 

Note the difference in color. 

I next test a part of each of these two solutions sepa- 
rately with ammonia, just as I did the copper solution in 
Ex. 91. 

Note the great difference in the two results. 

Do the two solutions contain the same or different sub- 
stances ? 

The Facts. — The iron chloride, made by hydrochloric 
acid, is green, while that made by aqua regia is yellow. 
When ammonia is added they behave very differently: the 
first gives a light green precipitate, while the last gives one 
that is reddish-brown. These differences lead us to think 
that there must be two different chlorides of iron, and 
this is true. 

The green chloride is EeCl 2 , called ferrous chloride. 

The yellow chloride is Fe 2 Cl 6 , called ferric chloride. 

In the names of the two chlorides of iron the endings ic 
and ous show the two proportions of chlorine, ic the larger 
and ous the smaller. With many other metals, also, 
chlorine forms both ic and ous chlorides. 

Ex. 97. — When the iron, in Ex. 93, took the copper out 
of the copper chloride, what else occurred ? To the liquid 
kept from that experiment add ammonia, and from the 
color of the result decide 

Whether it contains copper chloride or iron chloride. 

Whether it contains ferrous or ferric chloride. 



CHLORINE AND THE CHLORIDES. 



145 



You can then understand just what happened in Ex. 93. 
For if the ammonia gives the green precipitate, then fer- 
rous chloride is present, and the iron must have changed 
the copper chloride into it. Thus : 



CuCl 2 + 



Fe = - FeCL 



Copper chloride Iron Ferrous chloride 



Cu 

Copper 



Atoms of iron took the place of atoms of copper, and 
changed the copper chloride to the ferrous chloride. 

Hydrogen Chloride This is another name for hydro- 
chloric acid, — one of the strongest and most useful of all 
acids. It is made on a large scale from common salt by 
the help of sulphuric acid. On a small scale we may pre- 
pare it with the apparatus used for chlorine, leaving out 
only the drying-tube, as shown in Fig. 59. 

Ex. 98. — I put 50 cc. strong sulphuric acid in a, press 
its stopper home, and join its long tube with the side- 
neck. I leave b 
empty (it should 
be dry), close 
it with the stop- 
per and join to 

a. I put a strip 
of moist blue lit- 
mus-paper in c, 
and join it with 

b. The bottle d 
contains water, 
into which the 
tube from 




c is 



b~a,__ 

Fig 59- 

put with its end scarcely more than covered. Finally I 
put the materials, dry salt, 5 g., and strong sulphuric acid, 
10 cc, into the side-neck, and close it tightly. The reac- 
tion sets in at once ; but to keep it up, I apply a very gen- 



146 CHLORINE AND THE CHLORIDES. 

tie heat so that bubbles will be seen in a a little faster 
than one can count. The acid in a is used to absorb mois- 
ture which comes over with the gas ; the gas will be dried 
by the acid if it does not come over too fast. 

Xote the action of the hydrochloric acid on litmus. 

Note the color of the gas. 

What is the effect of the water in the bottle d? 

Ex. 99. — I remove the cork and tubes from flask b, and 
then invert the flask with its mouth in a vessel of water. 
The water quickly rises to almost fill the flask. 

How can you account for this result ? 

The Facts. — The reaction when sodium chloride, Na CI, 
and sulphuric acid H 2 S 4 . are gently heated is this : 

NaCl + H 2 S0 4 = HNaS0 4 + HC1 

The hydrochloric acid, H CI. is a colorless gas which in- 
stantly reddens litmus and dissolves with great freedom 
in water. The so-called hydrochloric acid, of commerce and 
the laboratory, is a solution of this gas in water. 

Composition of Hydrochloric Acid by Volume. — If 
hydrogen and chlorine gases are mixed, they will combine 
when exposed to light, and, by measuring the gases, it has 
been found that it takes just as many cubic centimeters of 
hydrogen as of chlorine. Pure hydrochloric acid contains 

1 volume of hydrogen and 1 volume of chlorine. 

But now, how much hydrochloric acid will these two 
volumes of its elements make ? It has been found that if 
10 cc. of hydrogen and 10 cc. of chlorine are used, there 
will be just 20 cc. of the hydrogen chloride made. 

One volume hydrogen and 1 volume chlorine make 2 vol- 
umes hydrogen chloride. 

Now compare this fact with another noted under the 



i 



CHLORINE AND THE CHLORIDES. 147 

composition of water, p. 56, and still another noted under 
the composition of ammonia, p. 90. 
We see that in the case of 

H CI, 2 volumes of the elements make 2 volumes of compound. 
II 2 0, 3 " " " " 2 

H 8 N, 4 " " " " 2 

Jnst two volumes of the compound gas is made every 
time ! The same thing is found true of other compound 
gases also. Take the five compounds of nitrogen and oxy- 
gen, for example : 

2 volumes X and 1 volume O make 2 volumes nitrous oxide. 



1 volume 


X 


' ; 1 volume ' 


< 2 


,; nitric oxide. 


2 volumes 


N 


" 3 volumes 4 


2 < 


; nitrous anhydride. 


1 volume 


N 


" 2 volumes ' 


- 2 ' 


' nitrogen peroxide. 


2 volumes 


N 


" 5 volumes " 2 " nitric anhydride. 



These are the results of experiments. And so, whether 
we have two volumes of the constituents, as in the second, 
or seven volumes, as in the fifth, there are just two volumes 
of the compound made when they combine. If we put 
all these facts into one statement, we have this law: The 
volume of a compound gas is two, whatever may be the 
number of volumes of the elements in it. 

Test for Chlorine and the Chlorides. — Let a drop of 
silver nitrate solution be added to a solution of chlorine 
or of any chloride, and a white cloud or precipitate will ap- 
pear. This white precipitate is silver chloride. It will 
become dark colored if left a little while in the sunlight. 
Try this test on several chlorides. 

THE CHLORINE GROUP. 

There are three other elements which are so much like 
chlorine, that the four are together called the chlorine 
group. They behave so nearly like chlorine, and their 



148 CHLORINE AND THE CHLORIDES. • 

uses are so much less important, that we need not stop 
long with them in our study. 

Bromine. — A little more than half a century after the 
discovery of chlorine — it was in the year 1826 — M. 
Balard, a French chemist, found another element, with 
properties much like those of chlorine. Its odor was 
found to be so strong that, in honor of this characteristic 
the element was called bromine. The word is from the 
Greek word ppcofjiog (bromos), which means stench. 

Bromine is not very abundant, but it does exist in the 
waters of some mineral springs, and in larger quantities 
in the waters of the sea. It is always found in combina- 
tion, and its compounds are called bromides. 

Bromine is a liquid, but a very gentle heat changes it 
to gas. It has a beautiful dark-red color. 

This element readily combines with hydrogen and with 
metals; in this respect it is like chlorine, and like that 
element it is able to remove colors and to destroy bad 
odors. 

Iodine. — M. Courtois was a chemical manufacturer in 
Paris. He was engaged in making soda, and was using 
the ashes of sea-weeds for this purpose. A dark-colored 
liquid was left in his kettles, and attacked the metal of 
which they were made. When some sulphuric acid was 
put with it, this liquid gave up a substance which, when 
heated, changed to a beautiful violet-colored vapor. It 
proved to be a new element, and it was called iodine. 
This, from the Greek word icodt^ (iodas), means violet- 
colored. 

Iodine is a constituent of sea-plants, as we may know 
from the story of its discovery. The sea contains it in 
small quantities, and so do the waters of some mineral 
springs. It is an element in sponges, and in oysters, and 
in some fishes. It is always found in nature, combined 
with other substances. 



CHLORINE AND THE CHLORIDES. 149 

Iodine is a solid. A gentle heat melts it, and a little 
higher temperature changes it into its beautiful vapor. 

Water dissolves it, but a single grain will take no less 
than 7000 grains of water to dissolve it. How small this 
proportion of iodine, and yet it gives to the whole body 
of the water a brownish-yellow color ! Alcohol will dis- 
solve it in large proportions. This solution in alcohol is 
the " tincture of iodine, 7 ' used in medicine. 

Iodine combines with hydrogen and with many metals. 
In this respect it is much like chlorine and bromine. Its 
compounds are called iodides. 

Some of its compounds with the metals are remarkable 
for their very brilliant colors (Ex. 13). 

But there is one effect of iodine which neither chlorine 
nor bromine can produce: it is the fine blue color it gives 
to starch. Thus : 

Ex. 100. — I boil a bit of starch in a half test-tubeful 
of water, and after it has become cold I add a little iodine- 
water, made by vigorously shaking a crystal of iodine in 
water. Note the blue color produced. 

Compounds of iodine do not blue the starch ; the experi- 
ment may be made with potassium iodide. But if one of 
these can be decomposed the free iodine will show itself 
by the color; the experiment may be made by adding drops 
of nitric-acid to the solution of potassium iodide, and then 
adding the starch. The test for free iodine is starch. 

The physician finds iodine very useful as a medicine. 

The photographer finds it very valuable in the art of 
picture-making. 

The element itself is sometimes used in medicine, but 
its compounds are more generally used in the arts. 

Fluorine. — This element is found in combination with 
the metals, and all attempts to get it free have failed. Its 
chemical attractions are so strong, that if it be set free it 



150 CHLORINE AND THE CHLORIDES. 

immediately combines with something else ; even with the 
substance of the vessel in which the work is done. And 
yet it is remarkable that this is the only element which 
is not known to combine with oxygen. Its strongest 
affinities are for hydrogen and the metals. We cannot 
say whether fluorine is a gas, or would be if out of 
combination, as chlorine is. It is supposed that it 
would be, because it is a much lighter substance than 
chlorine. It is only nineteen times heavier, while chlo- 
rine is 35.5 times heavier than an equal bulk of hydrogen. 

The mineral called fluor spar, CaF 2 , is the most abund- 
ant compound of fluorine. When this is treated with 
sulphuric acid the fluorine leaves the calcium, Ca, and 
combines with hydrogen. This gives a gas, — the hydro- 
fluoric acid, H F. This acid gas is useful in the art of 
etching glass; for wherever it touches glass the fluorine 
leaves the hydrogen to unite with the elements of the 
glass instead. 

Hydrogen Compounds. — Fluorine, chlorine, bromine, 
and iodine behave toward hydrogen very much alike. 
Each one forms a single compound with that element, and 
each one combines with the hydrogen, atom for atom. 
Their names and formulas plainly show this fact. Thus : 

Hydrochloric acid HC1 

Hydrobromic acid H Br 

Hydroiodic acid HI 

Hydrofluoric acid . . . H F 

This is a very interesting fact, for there is no other 
non-metal, besides these four, that will combine with hy- 
drogen atom for atom. In the case of oxygen, for example, 
the compound is water, H 2 0, in which an atom of oxy- 
gen takes two atoms of hydrogen. An atom of oxygen 
refuses, absolutely, to ever take any less than two of 
hydrogen. 



CHLORINE AND THE CHLORIDES. 151 

General Behavior. — These four elements behave very 
much alike in other respects. This is, to be sure, not quite 
so marked in the case of fluorine as in the other three, 
but in general they combine with the same elements and in 
the same proportions. And they are able to do the same 
kinds of work ; as, for instance, chlorine bleaches colors ; so 
does bromine, and iodine also, when in solution. 

Chlorine is a better bleacher than bromine, — it is more 
powerful, and bromine is a better bleacher than iodine. 
But they are all bleachers. 

Atomic Weights and Properties in general it is 

true in other cases, as well as in bleaching, that the chem- 
ical action of chlorine is more vigorous than that of 
bromine, and of bromine more vigorous than that of iodine. 
In fact, bromine will drive iodine out of combination and 
take its place, and chlorine will treat bromine in the same 
way. Now this order of chemical strength is just the 
order of their atomic weights, beginning with the smallest. 
Thus : 

Atomic weight of CI 35.5, with most vigorous chemical action. 
Atomic " " Br 80 " less " " " 

Atomic " " I 127 " least " " " 

Their forms, gaseous, liquid, and solid, are in the same 
order ; so are the densities of these elements. In fact, the 
properties of these elements seem to depend, in some way, 
on their atomic iv eights. 

EXERCISES. 

1. Study the actions of chlorides, bromides, and iodides on 

silver nitrate. 

1. Arrange three test-tubes, one with a little solution 

of sodium chloride, another with as much solution of 

potassium bromide, and another with as much solution of 



152 CHLORINE AND THE CHLORIDES. 

potassium iodide. Add silver nitrate drop by drop, shak- 
ing the tube vigorously after each addition, until a drop 
fails to make a precipitate. Describe the precipitates. 
]STote the effect of shaking them. Look carefully for some 
difference in their colors. 

Then expose the tubes to sunlight, or for some time to 
diffuse light, and note the changes which occur in the 
colors. 

2. Next test the solubility of these precipitates in am- 
monium hydrate. To do this, make a little fresh precipi- 
tate, and keep it from light as much as possible. When 
the precipitate has settled, decant the liquid, that is, pour 
it away carefully so as to leave the precipitate in the tube. 
Then pour upon it ammonium hydrate gradually, with 
shaking, until you can decide whether the precipitate dis- 
solves. Do they all dissolve? Does one dissolve more 
easily than another ? 

3. Write a brief statement of all the facts which you 
have discovered, noting particularly the points of difference 
among the three compounds. 

2. Study the action of chlorides, bromides, and iodides on 
starch. 

1. Make a very thin starch-water, by boiling a minute 
piece of starch in considerable water, and cooling the 
liquid. 

2. Dissolve a chloride, a bromide, and an iodide, each in 
water. 

3. To a part of each solution add a few drops of nitric 
acid, and afterward add a little of the starch-water. There 
should be a difference in color produced ; note it carefully. 

To another part of each solution add a little of the cold 
starch-water, without the nitric acid. By this means you 
can decide whether nitric acid is necessary to bring out the 
colors observed before. 



CHLORINE AXJ) THE CHLORIDES. 153 

4. Add the starch-water to hot solutions instead of cold 
ones, and let them become cold. By this means you will 
learn the effect of heat. 

5. Write a brief statement of all the facts which you 
have discoverd. 

Chlorine, bromine, and iodine behave so very much alike, 
that it is not always easy to distinguish their compounds 
one from another. And then, too, there is another class of 
compounds called cyanides, which might be mistaken for 
some of these. Still the "silver-nitrate," and the " starch 
test," will help one to identify these three classes of com- 
pounds. In the case of the nitrate test, the pure precipi- 
tates differ a little in color, and more in solubility in 
ammonia, — the chloride being easily soluble, the bromide 
much less so, and the iodide almost not at all. In the 
starch test, nitric acid must be used to decompose the com- 
pounds, because it is only the free iodine which gives the 
blue, and the free bromine which gives the brown color. 

3. Take a few substances from the teacher, or a friend who 
knows what they are, and see if you can decide whether 
each is a chloride, bromide, or an iodide. 



SULPHUR AND ITS COMPOUNDS. 



Native Sulphur. — Sulphur seems to have been known 
and used in the most ancient days of which we have any 
account. The element itself, and its compounds also, are 
very abundant in the earth. The element itself, or native 
sulphur, is found in the neighborhood of volcanos, or where 
these fire-mountains have been active in time past. Large 
quantities are taken from mines in Sicily ; in fact, a great 
part of the sulphur in commerce comes from this source. 

Native Sulphides. — Sulphur is found combined with 
metals in the rocks and soils almost everywhere. These 
compounds are called suty hides. 

The sulphide of iron is a good example. It is a brassy- 
looking substance, very common in many rocks. It is often 
found in the form of little cubes, as perfect as if they 
had been chiselled by an artist. Sometimes it is found in 
the form of thin, shining, yellow scales. It has been 
called " fool's gold," because the ignorant have been de- 
ceived by its color. It is iron disulphide, FeS 2 , and is 
commonly called iron pyrites. 

The sulphides are the substances from which the useful 
metals are often obtained. Lead, for example, is taken 
from the mineral called galena, but galena is the lead sul- 
phide, Pb S. Silver, copper, and zinc are also among the 
useful metals, found in the rocks in combination with 
sulphur. 

Preparation of Sulphur. — In its native state, as found 
in the mines of Sicily, sulphur is not combined with any- 
thing, but yet it is very .far from being ready for the mar- 
ket. It is not in combination, but it is mixed with a great 
deal of earthy impurities from which it must be separated. 

154 



SULPHUR AND ITS COMPOUNDS. 155 

This is easily done, because sulphur is easily changed into 
vapor by heat, while the earthy impurities are not. Let 
the mixture be heated, then, and the sulphur-vapor will 
pass away and leave the impurities behind. The vapor, 
being cooled again, is sulphur, which is very much more 
free from earthy matter than before. 

It is heated a second time to remove the impurities 
which the first process did not. This time the vapor is 
run into a large chamber, and it is condensed upon the 
cold walls in very fine powder. This powder is the " flowers 
of sulphur " which is so common. 

When the chamber is smaller, its walls become too hot to 
collect the powder, which then melts, and the liquid runs 
down upon the floor. It runs into channels in the floor 
which lead it out of the chamber into moulds. In this way 
the familiar sticks of " roll brimstone " are made for the 
market. 

Effects of Heat on Sulphur. Ex. 101. — I reduce a 
piece of brimstone to coarse powder and half fill a test-tube 
with it. I hold the tube in the hot air above the lamp-flame, 
and thus keep it from contact with too strong a heat, but 
lower it until I find the heat intense enough to melt the 
sulphur. The liquid should not be darkened, but be yellow 
and limpid. 

Ex. 102. — I place the tube with the limpid yellow liquid 
where it will not be shaken, and watch the liquid while it 
slowly cools. 

In what form does the sulphur solidify ? 

Ex. 103. — I now carefully re-melt the sulphur, and then 
make the yellow liquid a little hotter, — only a little. 

Note the change in color. 

I continue to heat the liquid gradually and incline the 
tube from time to time, and observe that the color deepens 
and the sulphur grows viscid until it refuses to flow at all. 



156 SULPHUR AND ITS COMPOUNDS. 

I then heat it still more, and notice that the half-solid 
sulphur re-melts. 

I continue to apply heat to rind out whether the sulphur 
can be boiled, and what is the color of the vapor. 

I then pour the liquid in a small stream into a vessel of 
cold water, and examine the sulphur after this sudden 
cooling. 

The Facts. — Sulphur at ordinary temperature is a 
bright yellow solid, but when heated a little hotter than 
boiling water (114.5° C.) it melts to a limpid yellow liquid. 
Some care is required to preserve this yellow r color, since 
it easily changes if the heat be much greater. 

At a higher temperature, about 132°, the sulphur begins 
to grow viscid as w^ell as dark colored. Darker and thicker 
it becomes as it gets hotter, until, at about 230°, it is almost 
black, and is so very viscid that it will not flow from the 
vessel even if turned bottom upward. Make the hot sul- 
phur still hotter, and the dark-colored, almost solid sub- 
stance grows less viscid again ; it will flow in the vessel 
very much like thick syrup. 

At a higher temperature, about 450°, the sulphur boils. 
The hot vapor is colorless, but if cooled a little it is con- 
densed and becomes yellow. 

Plastic Sulphur. — If melted sulphur, just below its 
boiling-point, be poured into cold water, it cools into a sub- 
stance which looks like India-rubber. If we handle it, we 
rind that it is like India-rubber in other things besides its 
color : it is tough and elastic. This unusual form of sul- 
phur is called plastic sulphur. It will not stay in this 
condition, but gradually it will become again yellow and 
brittle as at first. This plastic sulphur is almost as unlike 
the common form as if it were another element. In these 
two forms we find a good example of allotropism, p. 39. 

Crystals of Sulphur. — If melted sulphur, limpid and 



SULPHUR AND ITS COMPOUNDS. 157 

yellow, be allowed to cool slowly (Ex. 102), fine needle- 
shaped crystals will be seen to shoot out from the walls of 
the vessel. They will increase in number and size, until 
finally, when cold, the solid mass of sulphur will be made 
up of these slender prisms interlaced and crowded together. 

Crystals of sulphur are also found in nature, but their 
shape (rhombic octohedra) is quite unlike that of the arti- 
ficial crystals obtained by fusion. In these two forms of 
sulphur we have a good example of dimorphism, — the prop- 
erty in virtue of which a substance may crystallize in two 
distinct forms. Sulphur is called a dimorphorus element, 
because it crystallizes in two shapes. 

Artificial Sulphides A sulphide of copper can be 

made as follows : 

Ex. 104- — I prepare a small coil of fine copper wire, 
Xo. 30, by winding the wire around a small lead-pencil or 
glass tube. I put a few fragments of sulphur into a tube, 
and then insert the coil and heat the sulphur to boiling. 
Watch for any sign of chemical action, and notice that, 
once well started, it will run to the upper end of the coil 
without the further aid of the flame. 

Compare the substance of the coil now with the copper 
and the sulphur which were used. 

Ex. 105. — The experiment may be made by mixing 4 g. 
flowers of sulphur with 8 g. of fine copper-filings, and heat- 
ing this mixture in a test-tube. 

The Facts. — When copper and sulphur are heated to- 
gether they unite and form a compound which is grayish - 
black, and brittle. The lamp-flame brings them to the 
right temperature, when at once the action sets in. A 
vivid red glow begins, and goes quickly to the end of the 
coil or mixture. This glow is not due to the lamp-flame, 
because it goes on even if the flame is taken away. The 



158 



SULPHUR AND ITS COMPOUNDS. 



additional heat to make the glow must be caused by the 
chemical action itself. Thus : 

Materials. Products. 

Cu + S = C u S + heat 

Many other metals, like copper, will become sulphides 
when heated with sulphur. If a white-hot rod of iron is 
used to stir melted sulphur, the iron will become iron 
sulphide, and if zinc and sulphur are properly heated, zinc 
sulphide is obtained. 

These artificial sulphides are not always the same as 
the native sulphides of the same metals. This artificial 
sulphide of iron, for example, is very different from the 
native pyrites. It is Fe S, while the native sulphide is 
FeS 2 ; the first is the ferrous sulphide, while the second 
is the ferric sulphide. 

Hydrogen Sulphide. — The ferrous sulphide is very 
easily decomposed by acids. 

Ex. 106. — I put a piece of ferrous sulphide, 1 not larger 
than a grain of wheat, into a test-tube, and pour upon it 
1 cc. dilute hydrochloric acid (half water). 

Notice the effervescence : what does it show ? 

Notice the odor in the tube. 

Notice the color of the liquid when the action is over. 

Add ammonia to the liquid and compare with Ex. 96. 

The Facts. — By the action of the acid and sulphide a 
gas is set free with effervescence, and its bad odor — 
like that which arises from the putrefaction of certain 
things, such as eggs — proves this gas to be hydrogen sul- 
phide. The ammonia test suggests the presence of ferrous 
chloride in the liquid. Hence the reaction is as follows: 

FeS + 2 II CI = FeCl 2 + H 2 S 

1 This substance is sold in the form of " sticks," which is very 
much better than the powder or the granular form. 



SULPHUR AND ITS COMPOUNDS. 



159 



The H 2 S is the hydrogen sulphide : it is also called 
s u Ij)h it retted h ydrogen . 

This gas is found in the waters of " sulphur springs. 7 ' 
All the sulphur which such springs contain is in the form 
of this gas. They owe their nauseous taste and odor, and 
their medicinal value, to hydrogen sulphide dissolved in 
their waters. 

This gas is a powerful agent for changing the metals 
into sulphides ; no other substance is so valuable to the 
chemist for this purpose. 

Preparation and Properties. — In order to study the 
behavior of this gas without being annoyed by its escape 
into the room, we may employ our usual form of gas ap- 
paratus. 

Ex. 107. — Put 40 cc. water into a, Fig. 60, to cover 
the lower end of the long tube. Add a cubic centimeter 
of solution of lead 
acetate, and a drop 
or two of hydrochlo- 
ric acid to 40 cc. 
of water, and put 
the mixture into b. 
Into c put 40 cc. 
water containing 
some ar sen ions ox- 
ide solution, and 
several drops of 
acid, and into d put 
20 cc. dilute ammo- 
nium hydrate (half water). Connect the parts of the ap- 
paratus, and be sure that the joints are tight. 

Finally, put 10 g. ferrous sulphide, in small pieces, into 
the side-neck flask, and pour upon it 30 cc. of dilute hydro- 
chloric acid (half water), and stopper the flask at once. 




160 SULPHUR AND ITS COMPOUNDS. 

The air will be gradually driven out of the flasks, and 
then the H 2 S will begin to show its presence by its ac- 
tion on the liquids through which it passes. 

Note its color as seen above the liquids. 

Note the results of its action on the lead compound. 

Note its different action on the "arsenic." 

Note the effect of the ammonium hydrate. 

Let the action go on until the effervescence stops. Then 
take flask a out of the series, and transfer a little of its 
water to tubes for the following purposes. 

What is the odor of this water? 

What is the effect of adding to it drops of H CI and 
then of lead acetate ? 

What is the effect of adding to it drops of H CI and 
then of arsenic solution ? 

Does the water have the same effects as the gas itself ? 

The Pacts. — Sulphuretted hydrogen is a colorless gas 
which is dissolved by water quite freely (a). The gas in 
solution behaves just like the gas alone, readily changing 
metallic compounds into sulphides. 

This gas is also very soluble in ammonium hydroxide 
(e), but in this case the solution is not a simple one, as 
in water : there is chemical action between the two sub- 
stances, and the result is ammonium sulphide. 

Use in Analysis. — It is easy to see (flasks b and c) that, 
if one has a solution which contains either lead or arsenic, 
without knowing which, sulphuretted hydrogen will help 
him to decide, for lead sulphide is black while arsenious 
sulphide is yellow. So this gas is often used to identify 
the metals in the work of analysis. 

But it is still more often used by the chemist to separate 
two or more metals whose compounds are mixed. An 
example will show how this may be done. 



SULPHUR AND ITS COMPOUNDS. 161 

Ex. 108. — I mix 1 cc. strong solution of copper chloride 
and 1 cc. strong solution of zinc chloride, and then add 
10 cc. H 2 S solution freshly made (Ex. 107). I let the black 
precipitate settle and then acid drops more of the H 2 S 
solution, to see whether more precipitate forms. I must 
add the hydrogen sulphide as long as it ivill make the pre- 
cipitate, but when it refuses to do more I filter the whole 
into a clean tube or bottle. I now have the black pre- 
cipitate in the funnel, and the clear liquid in the vessel 
below. 

This liquid should contain all the zinc and none of the 
copper. Test it by adding a few drops of ammonium 
hydroxide : the presence of zinc and absence of copper 
is shown by a white precipitate, without the blue which 
copper would yield. 

The black precipitate should contain all the copper and 
none of the zinc. Test it by putting a little in a tube 
and warming it with a few droits of nitric acid to dissolve 
it, then adding a little water, and finally adding am- 
monium hydroxide. The copper will be shown by the 
familiar blue color. 

THE SULPHUR GROUP. 

There are three other elements whose chemical actions 
are very much like those of sulphur. These are selenium, 
tellurium, and oxygen. 

Selenium Selenium is a rare element, which is found 

in combination with some metals, such as copper and iron. 
These compounds are called selenides. The element is a 
solid. It burns in the air with a reddish-blue flame, and 
an odor peculiarly offensive, even worse than that of burn- 
ing sulphur. It is a conductor of electricity, if it be first 
melted and then slowly cooled, but not a conductor if 
cooled quickly. Its symbol is Se. 



162 SULPHUR AND ITS COMPOUNDS. 

Tellurium. — Tellurium is even more rarely found than 
selenium. The element is bluish-white, and has a fine 
luster. Like sulphur and selenium, it is found in the earth 
combined with metals, such as gold, silver, and lead. Its 
symbol is Te. 

Their Hydrogen Compounds. — Sulphur, selenium, and 
tellurium unite with hydrogen, and in the same propor- 
tions. Each one combines with the hydrogen, not atom for 
atom, but one atom for two. In this respect they are like 
oxygen. Their names and formulas plainly show this fact. 
Thus : 

Hydrogen oxide H 2 O 

Hydrogen sulphide H 2 S 

Hydrogen selenide H 2 Se 

Hydrogen telluride H 2 Te 

Xow these four are the only non-metals which combine 
with hydrogen in this w r ay — one atom with two. But 
these do so always. 

General Behavior. — These four elements act very 
much alike in other respects. They combine with the same 
things and in the same proportions. This is not quite so 
well marked in the case of oxygen, which stands a little 
apart from the rest ; but still the likeness is very strong, 
and these four form a well-marked natural group. 

Atomic Weights and Properties. — The order of the 
atomic weights in this group is as follows : 

O S Se Te 

16 32 79 125 

This is also the order of their specific gravities. When 
equal volumes are weighed, is found to be the lightest, 
and S, Se, and Te are heavier in this order. It is also the 
order of their melting-points ; oxygen melts at a very low 
temperature, S melts at about 114° C, Se at 217° ; and Te 



SULPHUR AND ITS COMPOUNDS. 



163 



at 500°. It is also the order of their energy in chemical 
action, that of being greatest and of Te least. The 
gradually varying properties of this set of elements stand 
in the order of their atomic weights. This is the second 
case of this kind (see p. 151). Are there other instances ? 
We shall see. 

^SULPHUROUS OXIDE AND ACID. 

Burning of Sulphur. — We have found (Ex. 8) that 
sulphur will burn freely in oxygen, with a rich blue flame, 
and that the product will dissolve in water, which will then 
redden blue litmus. We have also found (Ex. 43), that 
sulphur will readily burn in air. The product of combus- 
tion, in both cases, is sulphur dioxide, S0 2 , which is more 
commonly called sulphurous oxide. 

Preparation of S0 2 — This oxide is easily made by 
heating sulphuric acid with copper. 

Ex. 109. — I put 10 g. of copper, in small pieces, such as 
clippings of sheet-copper or wire, into the side-neck flask 




of the gas apparatus (Fig. 61), and pour upon it about 20 cc. 
of strong sulphuric acid. 



164 SULPHUR AND ITS COMPOUNDS. 

I put 15 cc. of water in a } 15 cc. of sulphuric acid in b, 
and 50 cc. of water in e, and I then join the series a, b, c, 
d, e, as usual, the long tube of each with the short tube of 
the one in front of it, and a with the side-neck. 

I now heat the side-neck flask with a small flame until 
effervescence begins, and afterwards just enough to keep 
the action going. The liquid will froth over if the heat is 
too strong. A little white vapor of sulphuric a'cid goes over 
into a, but the true appearance of the oxide should be seen 
in b, and in the other flasks. 

What is the color of sulphurous oxide ? 

Can you decide whether the gas is absorbed by H 2 in e? 

To discover the Properties of Sulphurous Oxide 

When the action is over I at once take all the flasks apart, 
and then examine the gas they contain. 

Ex. 110. — I thrust a strip of moist blue litmus-paper 
into a and leave it hanging, held by the stopper which I 
press in beside it. I suspend a strip of dry blue litmus- 
paper in the same way in b. Xote any difference in the 
action of the moist and dry gas. 

Ex. 111. — I lower the flame of a small taper, or of a 
splinter of wood, into the gas in «, and decide — 
W T hat is the effect of sulphurous oxide on fire ? 

Ex. 112. — If I boil a few small chips of logwood in 
water I get a rich wine-colored solution. I do this, and 
then, taking a test-tube half full of the colored water, I add 
some of the water from flask e. 

What is the effect of S 2 on this color ? 

Ex. IIS. — I transfer a little of the water from e to a 
dish or tube, and test it to learn — 
Whether it has the odor of the gas. 
Whether it is an acid. 



SULPHUR AXT) ITS COMPOUNDS. 165 

Ex. HJf. — At this point I take the tubes from c and d, 
and, closing the flasks with solid corks, I stand them aside 
for use at another time (Exs. 117, 118). I pour the brown 
liquid carefully out of the side-neck flask, leaving the almost 
black sediment behind, and then put in about 50 cc. of 
water, shake it well, and filter the whole into a dish or 
bottle. I keep this deep-blue liquid also for use at a future 
time (Ex. 121). Pour the liquids from a, b, e into the 
waste, take out their stoppers and stand the flasks mouth 
down in water, and leave them until the noxious gas is 
absorbed. 

The Facts. — Sulphurous oxide is a gas with no color, 
but possessing an odor of the most pungent and suffocat- 
ing kind, — the odor of a burning "Lucifer match. " The 
dry gas will not redden blue litmus, but when moist it 
will do so readily. It dissolves in water very freely, and 
this solution is an acid. It will also bleach the color of 
logwood and many other substances ; this the dry gas will 
not do. 

Sulphurous Acid. — The dry gas, and its solution, act 
quite differently on litmus, and also on coloring matter, 
and by this we know that the gas is not simply dissolved 
in the water, as in the case of chlorine, and of hydrogen 
sulphide, but that a chemical change has taken place. 

The fact is, that the gas unites with water ; 

S0 2 + H 2 = H 2 S0 3 

Sulphurous oxide Water Sulphurous acid 

and while the oxide itself is not an acid, its compound 
with the elements of water is. 

There are many other oxides like the sulphurous oxide 
in this respect, — they will combine with the elements of 
water, and thus form acids. All such oxides are called 
anhydrides. 



166 SULPHUR AND ITS COMPOUNDS. 

This one is called the sulphurous anhydride, because it 
unites with the elements of water, and becomes sulphur- 
ous acid. 

Bleaching. — The power of moist sulphurous oxide to re- 
move colors makes this substance very valuable for bleach- 
ing. Articles of straw, silk, and wool are bleached on a 
large scale, by first moistening them and then hanging 
them in chambers in which sulphur has been burned. 
The sulphurous oxide does not act on the color itself, but 
it decomposes water and sets free a part of the hydrogen. 
This hydrogen then acts on the colors, and changes them to 
colorless compounds. Unfortunately these colorless com- 
pounds will be decomposed on exposure to air and light, 
and then the color returns. 

Sulphurous oxide w r ill not burn, nor will it allow the 
combustion of anything else ; the fumes of burning sulphur 
will extinguish fire, 

SULPHURIC ACID AND THE SULPHATES. 

Some Properties of the Acid. — If we examine a 
specimen of strong sulphuric acid, which can be found 
in every laboratory, we find that it is a heavy oily-acting 
liquid. For this reason it is called oil of vitriol. If we 
taste it — which we must not do without first diluting it 
with a large quantity of water — we find it to be sourer 
than the strongest vinegar. If we touch it, we find our 
fingers smarting almost as if it had been fire. If we drop 
it upon our garments, we find them turning red wherever 
touched by it, and that, some days after, the red spots 
crumble into holes. 

When mixed with water the strong acid unites with it 
at once, and the mixture is heated as if by fire (Ex. 14). 
This violent attraction between the acid and water throws 
light upon some well-known facts, thus : 



SULPHUR AND ITS COMPOUNDS. 167 

Ex, 115. — I put 2 or 3 cc. of oil of vitriol into a test- 
tube and place in it the end of a clean pine stick. After 
a few minutes I find the wood to be as black as if it had 
been scorched. Indeed, the wood is changed very much 
as it would be by fire. For by fire a black coal is left, 
while the other elements are driven away. 

What are the elements in wood ? See p. 101. 
Which one of these is left behind by the acid ? 
Then which ones are taken out by it ? 
"Why does the acid extract these ? 

One of our earliest experiments showed the singular 
effects of this acid on sugar (Ex. 2), and now you can 
no doubt find in the composition of the sugar, and this 
property of the acid, a good explanation of that action. 
Do so. 

Some uses of Sulphuric Acid. — The chemist very 
often needs the gases, with which he works, to be per- 
fectly dry; he remembers this strong attraction between 
sulphuric acid and the elements of water, and makes his 
gas bubble through some of the acid. It comes off dry. 

Sulphuric acid is used in making a great many materials 
used in the arts, such as soap, soda, alum, and other kinds 
of chemicals. 

It is used also in coloring cloth, in printing calico, and 
then, at other times, it assists in the work of bleaching. 

Many thousands of tons a week, of sulphuric acid, are 
made and distributed over the world to be used for these 
and other purposes in the arts. The manufacture of sul- 
phuric acid is one of the most important industries. 

Test for Sulphuric Acid. — If, to any liquid which 
contains this acid, a solution of barium chloride is added, 
a white precipitate will be made, which cannot be dis- 
solved by water or acids. Thus : 



168 SULPHUR AND ITS COMPOUNDS. 

Ex. 116. — To half a test-tube full of water I add a drop 
of H 2 S 4 , and a half cubic centimeter of H CI, and then I 
add a solution of barium chloride (Ba Cl 2 ) drop by drop. 
The white precipitate (BaS0 4 ) which comes, in spite of 
the hydrochloric acid, shows the presence of H 2 S0 4 . Try 
this test on a solution of any of the sulphates. 

The Manufacture of Sulphuric Acid The process 

is founded on a few simple facts, which we can easily 
demonstrate, and for this purpose we have the flasks full 
of S 2 kept over from Ex. 114. The S G 2 may be made by 
burning sulphur in oxygen (Ex. 8 ), or in air (Ex. 43), but 
we ma}' use that already made in the other way. The 
question is now, How can this sulphurous oxide be changed 
into sulphuric acid ? 

Ex. 117. — I wet a shaving or splinter of wood with 
strong nitric acid and thrust it into the sulphurous ox- 
ide of flask cl (Ex. 114), and leave it there awhile. 

Notice the colored fumes which are produced. 

What is the meaning of these ? See Ex. 62. 

It may be well to insert the splinter, wet with nitric 
acid, a second time. But finally I take it out, pour 10 ec. 
of water into the flask, and shake it well, to dissolve as 
much as possible of the contents, then pour it into a test- 
tube and label it d. 

Ex. 118. — And now to find out whether the sulphur- 
ous oxide has been changed by the nitric acid I will dis- 
solve the gas, which still remains in flask c (Ex. 114) in 
10 cc. water, and then compare this solution with the 
other, labelled d, in this way: I first add a half cubic 
centimeter of hydrochloric acid, and then add drops of 
barium chloride, to each of my two solutions. 

Note the difference in results. 

What substance did the solution d contain ? 



SULPHUR AND ITS COMPOUNDS. 169 

The Changes. — When we bring sulphurous oxide and 
nitric acid together yellowish-red fumes appear (Ex. 117), 
and by these colored fumes we know that the nitric acid is 
being decomposed. Sulphurous oxide in water will yield 
no white precipitate with a mixture of hydrochloric acid 
and barium chloride, but after this action of nitric acid the 
solution will (Ex. 118). By this we know that the S 2 
has been so changed that its solution in water is sulphuric 
acid. 

If now we could only take the water out of the sul- 
phuric acid again, w r e could see what the S0 2 had been 
changed into. Unfortunately we cannot do this by experi- 
ment, but, fortunately, we can represent the process by 
formulas, as, in arithmetic or algebra, we often show by 
signs, the work which we do not actually do. From sul- 
phuric acid, H 2 S 4 , let us subtract water, H 2 0. 

H 2 S0 4 -H 2 = S() 3 

It must have been S 3 which, when dissolved in water, 
gave the sulphuric acid which we found in d, and hence 
the S 2 must have been changed into S 3 by the nitric 
acid. 

This S 3 is called sulphuric oxide. It is also called sul- 
phuric anhydride, because it combines with water to make 
sulphuric acid. 

The Facts. — What, then, are the facts which we have 
found ? They are as follows : 

1. The burning of sulphur yields sulphurous oxide. 

2. Sulphurous oxide will take oxygen from nitric acid 
and become sulphuric oxide. 

3. Sulphuric oxide dissolves in water and becomes sul- 
phuric acid. 

Application of These Facts. — These are the facts 
on which the manufacture of sulphuric acid is founded. 



170 SULPHUR AND ITS COMPOUNDS. 

In the actual process there are a few others, but for the 
full details you may refer to some larger chemistry. 1 

The acid is made in immense lead-lined chambers. Such 
a chamber may be 100 feet long, 20 feet wide, and almost 
as high as it is wide. Sulphurous oxide goes over into 
this chamber from a furnace where sulphur, or iron 
pyrites, is burning. Nitric acid, made on the spot, also 
enters the chamber, while jets of steam are blown in, and 
a full supply of air is kept up. 

The acid, which is made in this chamber, is too dilute 
for use, and it is made stronger by evaporation in lead 
pans, and then still stronger by evaporation in vessels of 
glass or platinum. These must be used instead of lead 
pans toward the last, because the strong acid will corrode 
the lead. 

The Sulphates. — The salts made by sulphuric acid are 
called sulphates. We may study these as follows : 

Ex. 119. — To make Zinc Sulphate. — I dilute some 
strong sulphuric acid by pouring 5 cc. of it into 40 cc. of 
water contained in a wide-mouth bottle, and drop into 
this small pieces of zinc. I let the action go on until the 
acid is used up, adding more zinc if necessary. When the 
effervescence has almost stopped, with zinc still left in 
the bottle, I filter the liquid to get rid of the black flakes 
which come from impure zinc. I next evaporate the liquid 
to one-half its bulk, and then let it cool. While it cools, 
crystals will be seen forming in the liquid. These crystals 
are zinc sulphate. 

Ex. 120. — To make Ferrous Sulphate. — I make 
some dilute sulphuric acid, as in the last experiment, and 

1 In Roscoe and Scliorlemmer, Vol. I. pp. 319-338, is a full 
account. In Cooley's Text-Book of Chemistry, p. 108, the reactions 
are given briefly. 



SULPHUR AND ITS COMPOUNDS. 171 

drop into it small iron nails, such as small "tacks." I 
cover the bottle with a plate of glass or a square of heavy 
paper, and, after the action has gone on for some time, 
I lift the cover, and at the same time bring a match-flame 
to the month of the bottle and discover 

What gas is set free by the action ? 

When the action is over I filter the liquid, and then 
evaporate it down to half its bnlk, and let it cool. If the 
evaporation has gone far enough, crystals will appear. 
These crystals are ferrous sulphate. 

Ex. 121. — To make Copper Sulphate. — For this 
purpose the strong acid is needed instead of the dilute, 
and heat must be used. This work was done in experi- 
ment 109, and if the deep blue liquid has been kept (Ex. 
114), we need not now repeat the experiment. Sulphurous 
oxide was set free instead of hydrogen, and the blue liquid 
contained the copper sulphate. Perhaps by this time blue 
crystals have made their appearance, but if not, I evaporate 
the liquid to smaller bulk and let it cool. The blue crystals 
are copper sulphate. 

Ex. 122. TO PROVE THAT THE BLUE CRYSTALS ARE 

Copper Sulphate. — I dissolve a crystal in water and 
then add ammonia, as in Ex. 91, and also into another 
portion of the solution I put a piece of iron. 

What are the proofs that the blue crystals are a com- 
pound of copper ? 

I dissolve another crystal and add a little hydrochloric 
acid and barium chloride (Ex. 116). 

What is the proof that the blue crystals are a compound 
of sulphuric acid? 

But a compound of copper and sulphuric acid must be 
the copper sulphate : the crystals are copper sulphate. 



172 SULPHUR AND ITS COMPOUNDS. 

Different Ways to make Sulphates. — Many sulphates 
may he made by the action of the sulphuric acid on the 
metals directly. In the case of zinc and iron the action 
goes on in the cold, and yields hydrogen beside the sul- 
phate. But in the case of copper, heat must be used to 
produce the sulphate, and sulphurous oxide and water, in- 
stead of hydrogen, are set free. 

Silver, mercury, and some other metals are like copper 
in this respect. When heated with strong sulphuric acid 
they yield sulphates, sulphurous oxide, and water. 

The sulphates may be made also by letting the acid 
act on the oxides or the hydrates of the metals, instead 
of on the metals themselves. 

It is also found that this acid will sometimes yield two 
salts of the same metal. 

It will do this with sodium, for when the acid is gently 
heated with common salt, as in Ex. 98, we get one salt 
of sodium, but when the heat is much stronger we get 
another. How can this be ? Well, we see that the mole- 
cule of the acid, H 2 S0 4 , has two atoms of hydrogen, and 
if the heat be gentle an atom of sodium, Na, takes the 
place of only one of them, and we have NaHS0 4 , but if 
the heat be strong both atoms of hydrogen are driven out 
by two of sodium, and we get Xa 2 S0 4 . 

The first, NaHS0 4 , is the acid sodium sulphate. 
The second, Na 2 S0 4 , is the normal sodium sulphate. 

These two kinds of salts may come from any other 
acid in whose molecules there are two atoms of H, which 
may be driven out by a metal. All such acids are 
called dibasic acids. Sulphurous acid, H 2 S0 3 , and carbonic 
acid, H 2 C0 3 , are dibasic. They are dibasic, not because 
they have two atoms of H in a molecule, but because they 
have two atoms of H which metals can displace. 



SULPHUR AND ITS COMPOUNDS. 173 

Acetic acid, H 4 C 2 2 , is monobasic. Its molecule con- 
tains four atoms of H, but with metals it will give up 
only one. 

An acid salt is one which still contains a, part of the hy- 
drogen which a metal can displace. A normal salt is one 
which contains none of the hydrogen which a metal can 
displace. The normal salts are generally neutral to litmus- 
paper, and are often called neutral salts. 

OTHER SULPHUR OXACIDS. 
The sulphurous and sulphuric acids are the most impor- 
tant oxygen acids of sulphur ; but besides these two there 
exists no less than six others. Look at their names and 
formulas. 

Hyposulphurous acid, H 2 S 2 ; Dithionic acid, H 2 S 2 6 
Pyrosulphuric acid, H 2 S 2 7 ; Trithionic acid, H 2 S 3 6 
Thiosulphuric acid, H 2 S 2 3 ; Tetrathionic acid, H 2 S 4 6 

Only one of these needs to be noticed any further at 
present, and that is the thiosulphuric acid. The sodium 
salt of this acid is very useful in photography : it dissolves 
away from the glass or paper the silver salts which have 
not been acted upon by light, and which, if left, would 
cause the picture to blacken. It is known as " hyposul- 
phite of soda/' but its true name is sodium thio sulphate. 

EXERCISES. 

1. Study the action of dilute acids on sulphides, sulphites, 
and sulphates. . 
1. Put a little of the powder of some specimen of each 
of these compounds into a tube, moisten it with water, and 
add a little dilute hydrochloric acid. Watch for efferves- 
cence, or any other evidence of chemical action. Notice the 
odor of any gas which may be set free. If no action begins 
soon, heat may be used. 



174 SULPHUR AND ITS COMPOUNDS. 

2. Use dilute sulphuric acid, making the experiments 
in the same way. 

3. Write a brief statement of your results, pointing out 
the differences in the behavior of these three kinds of com- 
pounds. 

2. Study the action of barium chloride on sulphites and sul- 

phates. 
i. Add drops of barium chloride to a solution of a sul- 
phite and to a solution of a sulphate. Then compare the 
precipitates which appear. 

2. Learn, by experiment, whether these two precipi- 
tates are alike soluble in hydrochloric acid. 

3. See whether both these precipitates will appear if 
you add the hydrochloric acid to the solutions before you 
add the barium chloride. Compare Ex. 118. 

Jf.. Write a brief statement of your results, pointing out 
the difference in the behavior of the sulphites and the 
sulphates. 

3. Take from the teacher \ or a friend who knows what 

they are, a few substances, and see if you can decide 
whether each is a sulphide, a sulphite, or a sulphate. 



PHOSPHORUS, AND THE NITROGEN GROUP. 

In 1669 a man by the name of Brandt, in Hamburg, was 
making experiments, hoping to find the "philosopher's 
stone," by the touch of which he would be able to turn 
any substance into gold. What he actually did find was 
a waxy-looking solid, yellow by daylight, but shining 
with a pearly white light in the dark. It burned furi- 
ously at the least provocation by warmth, and, on the 
whole, was so strange in its actions that the superstitious 
chose to name it "The Son of Satan." It proved to be an 
element^ and it has since been known as phosphorus. 

Properties. — Phosphorus comes to market in the form 
of round "sticks," four or five inches long, and about 
a half-inch in diameter. In color it is like yellow wax, 
but it is much harder than that substance, although soft 
enough to be easily cut with a knife. 

Its most remarkable property is its strong attraction for 
oxygen. If brought into the air it begins at once to unite 
with oxygen, and waste away by a "slow combustion." 
But if gently heated at the same time, its combustion 
becomes rapid and furious. 

To rub it with the warm fingers will inflame it. The 
friction of a knife-blade in cutting it will sometimes pro- 
duce heat enough to set it on fire. 

Such a substance can be safely handled only when it is 
under water. It is kept under water, and it ought to be 
cut under water, to avoid accident. 

This element is a powerful poison. 

Red Phosphorus. — Let some phosphorus be put into 
a vessel full of carbon dioxide or nitrogen, which will 
not act upon it, and then let heat be applied. In this 

175 



176 PHOSPHORUS, AND THE NITROGEN GROUP. 

case the phosphorus will not burn, no matter how hot 
it becomes. But at a temperature of 240° C. a curious 
change takes place. "The melted phosphorus becomes 
solid, opaque, and of a deep red color." It is phosphorus 
in an allotropic form. 

This " red phosphorus " may be exposed to the air and 
handled with very little danger. 

The common and the red are not the only allotropic 
forms in which this extraordinary element exists. There 
is a white and flaky form, lately discovered by Remsen, 
and a black variety has been described by Thenard. 

Matches. — Phosphorus is used, in large quantities, in 
making friction-matches. These are of several kinds, 
among which is the sulphur (" Lucifer " ) match, the par- 
affine match, and the safety match. 

The sulphur match is made by dipping the end of a pine 
stick in melted sulphur, and then into a paste made of 
phosphorus and a little nitre, KN0 3 , mixed in gum-water. 
Now, by rubbing the end of the match, we produce heat 
enough to set the phosphorus on fire ; the burning of the 
phosphorus produces more heat, by which the sulphur is 
set on fire, and then the sulphur burning with still more 
heat sets fire to the wood. 

The paraffine match is made in the same way, but par- 
affine is used instead of sulphur. 

In this way the troublesome odor (S 2 ) of burning 
sulphur is avoided. Sometimes potassium chlorate is used 
in the mixture, and then the match burns with a slight 
explosion. 

The safety-match has no phosphorus in its tip ; this 
element is spread on the side of the box instead. Red 
phosphorus is used. The match-stick is tipped with a 
mixture of sulphur or antimony sulphide, and potassium 
chlorate, and sometimes red lead or some other coloring 
substance is added. 



PHOSPHORUS, AND THE NITROGEN GROUP. Ill 

To "light" this match, it must be rubbed against the 
phosphorus surface of the box. 

Phosphorus Oxides. — There are two compounds of 
this element with oxygen. 

Phosphorus oxide P 2 3 

Phosphoric oxide P 2 5 

The first is made when phosphorus is simply exposed 
to the air. The second is made by burning phosphorus 
in oxygen or air. 

Let a small piece of phosphorus be hung, by a fine wire, 
inside a bottle ; white vapors of P 2 3 will fall from it and 
slowly fill the bottle. If then a little water is shaken in 
the bottle, some of these vapors are dissolved, and by 
adding a few drops of blue litmus solution, we prove the 
presence of an acid. Thus: 

Phosphorus oxide . . P 2 3 -f- 3 H 2 — 2 H 3 P 3 . . Phosphorus acid. 

Let a small piece of dry phosphorus be placed on a little 
cup on a plate. Let it be touched with a hot wire, and 
immediately covered with a dry glass jar. Clouds of milk- 
white vapor are quickly formed, and, if everything is dry, 
snow-white flakes will soon be seen, some clinging to the 
walls of the jar, others falling like snow upon the plate. 
This snow-white solid is phosphoric oxide, P 2 5 . 

Let a little water be poured on the plate, and the white 
solid will instantly dissolve with a hissing sound, like the 
sound of a hot iron in water. A little blue-litmus is red- 
dened by this solution, proving the presence of an acid. 
Thus: 

Phosphoric oxide . . P 2 5 + 3 H 2 O = 2 H 3 P 4 . . Phosphoric acid, 

There is a third acid in this series ; it is the hypo- 
phosphorus acid, H 3 P0 2 . But of these three we shall 



178 PHOSPHORUS, AND THE NITROGEN GROUP. 

notice further only the phosphoric acid, which is important 
on account of its useful salts, — the phosphates. 

The Phosphates. — These are found in rocks and soils, 
in plants and in animals. It is in the form of phosphate 
that phosphorus exists most largely in nature. We find 
it more abundant in the seeds of plants than in other parts, 
and in the brain, the blood, and the bones of animals ; and, 
accordingly, we find that the phosphates are much used to 
fertilize soils on which grain is to grow, and that they 
are also needful constituents in the food of man. 

Manufacture of Phosphorus. — Phosphorus is itself 
extracted from bones. Almost half the weight of the 
bones in animals is calcium phosphate, Ca 3 (P0 4 ) 2 , and 
about one-fourth of the weight of this phosphate is pure 
phosphorus. 

If the skeleton of a man weighs 12 lbs. it contains about 
one and a half pounds of this element. 

To obtain phosphorus from bones they are first burned ; 
in this process they become very white and very brittle. 
They are afterwards crushed to powder ; this powder is 
called bone-ash, and it is chiefly calcium phosphate. 

From the bone-ash the phosphorus is obtained 1 by 

1. Treating it with sulphuric acid. 

2. Evaporating the solution to dryness. 

3. Heating the residue nearly to redness. 

4. Heating to redness with charcoal. 

ARSENIC. 

The element arsenic is a solid substance with a steel- 
gray color, and a luster like the metals. It is very brittle 
and easily powdered. Its powder is sometimes sold under 
the false name "cobalt," to be used as a fly-poison. 

1 For details and explanations consult Koscoe and Sehorlemmer, 
Vol. I. p. 460. 



PHOSPHORUS, AND THE NITROGEN GROUP. 179 

This element is sometimes found in the earth not com- 
bined with anything, but such native arsenic, as it is called, 
is not common. It is mostly found in combination with 
metals and sulphur. 

In Silesia, Germany, there is found a mineral which con- 
tains arsenic with iron and sulphur ; it is called mispickel, 
and its formula is Fe As S. This mineral is the source 
from which most of the arsenic of commerce is obtained. 

The chief use of arsenic is in making shot. A small 
quantity of the element is melted with the lead. Lead 
alone is too soft; the arsenic hardens it. 

Arsenous Oxide. — This is the principal compound of 
arsenic in commerce. Its formula is As 2 3 , and it is also 
called arsenic trioxide, because its molecule contains three 
atoms of oxygen. In the drug-stores it is often called 
white arsenic, but more generally simply " arsenic." 

This oxide is made directly from arsenical pyrites, — 
another name for mispickel. 

To get the oxide from mispickel the mineral is roasted, 
that is to say it is heated in a current of air. The hot oxy- 
gen of the air takes the arsenic from the hot mineral, and 
the two elements combine ; arsenous oxide is the result, 

This substance is a white solid ; it can be dissolved in 
hot water, in cold water not so well. Its solution is almost 
tasteless and colorless, and without odor. It is a most 
fearful poison. 

But while this compound is so fatal to the life of an 
animal, it has a strange power to prevent decay. It is 
used to destroy rats, mice, insects, and sometimes for the 
terrible purpose of taking the lives of men. On the other 
hand, it is made to do good service in the preservation of 
the stuffed or dried objects of natural history to be found 
in museums. 

Arsenous oxide is an anhydride, that is to say, it be- 



180 PHOSPHORUS, AND THE NITROGEN GROUP. 



comes an acid by combining with the elements of water. 
By so doing it forms arsenous acid. Thus : 



As 2 3 



3 IL O 



2H 3 As0 3 



From this arsenous acid, H 3 As0 3 , a large number of 
salts, — the arsenites, may be made. Sodium arsenite is 
very useful in calico-printing ; it helps to " fix " the color, 
— in other words, prevent its fading. The common Paris- 
green is copper arsenite and copper acetate together. 

Arsenic Oxide. — There is also arsenic oxide ; its for- 
mula is As 2 5 . It is, like the other, an anhydride, for with 
water it yields arsenic acid, H 3 As0 4 . 

Arsenic and Hydrogen. — There is one compound of 
these two elements, a gas called arshie. It is made by the 
action of nascent hydrogen on a soluble compound of arsenic. 

It is very poisonous ; Gehlen, who 
discovered it, lost his life by acci- 
dentally breathing a bubble of this 
gas. It burns freely, and, if made 
in the laboratory, it should be burned 
as fast as it forms. 

Ex. 123. — To make and burn 
this gas I use the simple hydrogen- 
flame apparatus of Ex. 20, shown 
again in Fig. 62. Before putting 
the zinc into the hydrochloric acid 
in the mortar to make the hydro- 
gen, I dissolve a little arsenous 
oxide in water, by putting a very 
little of the powder — not more 
than will lie on the tip of a penknife-blade — into one or 
two cubic centimeters of water in a test-tube and boiling it. 
I then drop several fragments of zinc into the dilute 
acid in the mortar, and at once lower the funnel to cover 




Fig. 62. 



PHOSPHORUS, AND THE NITROGEN GROUP. 181 

them. Hydrogen is rapidly set free. It drives the air out 
of the apparatus, and when this is done I set fire to the 
jet. I now hold the bottom of a clean, dry porcelain dish 
right across the flame for a moment ; no dark stain should 
be left upon it. 

Then I pour the arsenous oxide solution into the mortar. 
Very soon the color of the flame becomes bluish-white. 
Again I press the cold porcelain for a moment down into 
the flame ; a lustrous brown stain is left upon it. I let 
the flame play on other parts of the dish, touching it here 
and there on the inside also. A large surface may be thus 
covered with the brown arsenical mirror. 

At the moment when hydrogen is set free by the zinc 
it attacks the arsenous oxide and changes the arsenic into 
arsine, AsH 3 , and its oxygen into water. 

The arsine burns with a livid flame, thus: 

2AsH 3 + 60 = As 2 3 + 3H 2 

arsenous oxide and water being the products of the action. 
But the cold porcelain cools the flame, and then only the 
hydrogen of the arsine burns, while the arsenic is deposited 
on the dish in the form of a lustrous mirror. This mirror 
will appear, even when the quantity of arsenic used in the 
experiment is astonishingly small. In fact, this experi- 
ment is a most excellent way of testing for arsenic in any 
suspicious substance. It is known as Marsh's test. 

The chemist has studied the compounds of arsenic, until 
he has so well learned their characters, that he can tell with 
great certainty whether they are present in a substance or 
not, and Marsh's test is his most trusted method. It is 
true that antimony will also give a stain on porcelain in 
the same way, but its color is velvety black, and there are 
other well-marked differences which are well known to 
every practical chemist. 



182 PHOSPHORUS, AND THE NITROGEN GROUP. 



THE NITROGEN GROUP. 

Phosphorus and arsenic are much alike in their chemi- 
cal actions, and in some things both resemble nitrogen : 
these three are the members of the nitrogen group of non- 
metals. 

Their Hydrogen Compounds. — These elements unite 
with hydrogen, and in the same proportions. The names 
and formulas of their compounds plainly show this fact. 
We have 

Ammonia (amine) ■. . H 3 N 

Phosphine H 3 P 

Arsine H g As 

We see that, in this group, each element unites with 
hydrogen, one atom for three. In other respects the 
resemblance among them is not so striking as it is in the 
chlorine group or in the sulphur group. 

The order of their atomic weights is as follows: 

N P As 

14 31 75 

This is also the order of their densities. The strength 
of their attraction for hydrogen is less, as the atomic 
weight is greater, in the same order. But among these 
elements the relation of properties to atomic weights is 
not so close as in the cases of the chlorine and the sul- 
phur groups. 



SLLICOX, AND THE CARBON GROUP. 

Silicon. — The element silicon is in many respects very 
much like carbon. 

It is usually a dark-colored powder, but it has two other 
forms, which are a little like graphite and diamond. 

Silicon, next to oxygen, is the most abundant element 
in the world, but it is never found alone ; it is combined 
with oxygen, and the two are not easily separated. Im- 
mense quantities of silicon, in this condition, are hidden in 
the sandstone rocks, so very common, yet very few persons 
who are not chemists have ever seen the element itself. 

Its Oxide. — The compound of silicon and oxygen is 
known as silica. Its true chemical name is silicon dioxide ; 
its formula is Si0 2 . Common sand is chiefly silica, and 
the sandstone rocks are masses of silica, mixed with many 
impurities to be sure, but chiefly silica. And besides, there 
are many purer forms, such as the following : 

Flint is a kind of very hard stone which is sometimes 
white, sometimes brown or black, but it is always silica, 
and a much purer form than sandstone. In some places 
very fine transparent diamond-shaped crystals are found ; 
they are called rock-crystal, and consist of pure silica. 
The common name of these hard varieties of silica is 
quartz. 

The beautiful amethyst is quartz crystal, with a delicate 
purple color. 

The precious opal, the crysoprase, and the bloodstone 
are little else than silica. 

Jasper is a very fine-grained form of silica, colored gen- 
erally red, but sometimes black. 

183 



184 SILICON, AND THE CARBON GROUP. 

The agate is a form of silica in which many tints of 
color are delicately arranged in stripes or bands. When 
the colors are few and very regularly arranged the agate 
is called an onyx. When the color is uniform, and a 
pearly white, the stone is a chalcedony, but when red it 
is called carnelian. 

THE CARBON GROUP. 

Silicon behaves very much like carbon in its chemical 
actions. The two are much more like each other than 
like any other non-metals, and they together are called 
the carbon group. 

Their Hydrogen Compounds. — These elements unite 
with hydrogen in the same proportions. They yield 

Methane (carbon hydride) C H 4 

Silicon hydride Si H 4 

We see that, in this group, each element unites with 
hydrogen, one atom with four. 

Their Oxygen Compounds They are not only alike 

in their combination with hydrogen, but also with oxygen, 
for we have carbon dioxide, C 2 , and silicon dioxide, Si 2 . 
And then, just as from carbon dioxide we get carbonic 
acid, by its union with water, thus : 

C0 2 + H 2 = H 2 C0 3 

The dioxide Water The acid 

so from silicon dioxide we get silicic acid, 
Si0 2 + H 2 = H 2 Si0 3 

The dioxide Water The acid 

The likeness does not stop here, for just as carbonic 
acid yields salts — the carbonates, so silicic acid yields 
salts — the silicates. 

The Silicates. — These salts are very abundant in na- 



SILICON, AND THE CARBON GROUP. 185 

ture, and very useful in the arts. The natural silicates 
occur in soils : clay is one of them. They also make up 
large rock masses : the slates are of this kind. Clay and 
the slate rocks alike are made chiefly of aluminum silicate. 

Artificial silicates are easily made. It is only necessary 
to melt together some silica, — say fine white sand, and 
potassium, or sodium, or calcium carbonate, to produce 
the potassium, sodium, or calcium silicate. These arti- 
ficial silicates are called glass. 

In each different kind of glass there are at least two 
kinds of silicate. In common " window glass " there are 
sodium and calcium silicates ; in " flint glass " there are 
potassium and lead silicates. Most ornamental glassware, 
such as vases, fine goblets, and decanters, are made of 
flint glass. 1 

BORON. 

The Element. — The element boron can be obtained 
in two forms ; as a dark-brown powder and as fine crys- 
tals, almost as hard as diamond. It is never found free 
in nature, but some of its compounds are quite abundant. 
The most interesting are boric acid and borax. 

Borax. — There is a lake in California (Borax Lake) 
whose waters hold a large quantity of borax in solution, 
and borax for the market is obtained by evaporating this 
water. It comes out in the form of a mass of white 
crystals. The chemical name of this substance is sodium 
biborate. But the pure and dry biborate is not quite the 
same as the crystals, for they hold a large portion of water 
in combination, while the biborate has none. 

This is shown by the formulas, — 

Sodium biborate Xa 2 B 4 7 

Borax crystals Na 2 B 4 7 -f 10 H 2 O 

1 Roscoe and Schorlemmer, Vol. II., Pt. L, pp. 462 to 490. 



186 SILICON, AND THE CABBON GBOUP. 

Now, this water is a part of the crystal, for if we drive 
it away by heat the borax is no longer crystalline. This 
water is, therefore, called the water of crystallization. The 
crystals of a great many other things also hold water of 
crystallization. 

Ex. 12 Jf. — I make a solution of 5 g. of borax in 20 cc. 
of hot water in a porcelain dish, and then acid to it, in 
small portions, 1 cc. strong sulphuric acid. I let this stand 
until cold. Then notice and describe the crystals which 
form. Are they crystals of borax? 

Ex. 125. — To answer this question I put some of the 
crystals into one porcelain dish, and as much borax into 
another, and pour upon each 10 cc. of strong alcohol. I stir 
them well, and then fire them both with a match-flame, and 
notice the color of the flames, especially around the edges. 

What evidence that the crystals are not borax ? 

Boric Acid. — Borax is changed to boric acid by the 
action of strong sulphuric acid. Boric acid when dry ap- 
pears in the form of glistening scale-like crystals (Ex. 124). 
These dissolve in alcohol, and tinge the flame of alcohol 
with green (Ex. 125). 

Boric acid is sometimes made on a large scale in this 
way, that is by the action of a strong acid on borax. But 
it is also obtained by evaporating natural waters which hold 
it in solution. Such water is found in Tuscany. It is in 
a volcanic region, and jets of volcanic steam, out of the 
earth, are directed into this water. The water evaporated 
by the volcanic heat leaves boric acid. 

No Hydrogen Compound. — Boron is the only non- 
metal which does not combine with hydrogen. We have 
seen that elements, which combine with hydrogen in the 
same way, are very much alike also in most of their chem- 
ical actions. Now here is an element which seems to have 



SILICON, AND THE CARBON GROUP. 187 

no disposition at all to unite with hydrogen, and, curiously 
enough, we find it standing apart from all the other non- 
metals in other respects too. When free, it is a little like 
carbon and silicon. In some of its properties it resembles 
the nitrogen group ; in others it is more like the metals 
than the non-metals. 

Boron does not fairly belong to either group of non- 
metals, but on the whole it stands nearer to the nitrogen 
group than to others, and it is usually named in the list 
of that group. 

But, in both its forms, it differs from the members of 
that group. For example : the crystallized variety will 
not readily combine with oxygen, while the elements of 
the nitrogen group, except nitrogen itself, will ; and the 
other variety — the brown pow^der — w^hen heated to red- 
ness, will combine with nitrogen ; this the other members 
of the nitrogen group will not do. 



VA]LE]SrCE. 

We have seen that every one of the non-metals, except 
boron, will combine with hydrogen. But we have found 
that they do not all combine with it in the same propor- 
tions. In some cases they combine with it, atom for atom 
(p. 150), in others one atom for two (p. 162), and in other 
cases the proportions are still different (pp. 182, 184). 
What is the meaning of this ? 

A Difference in Atoms The proportions of the ele- 
ments, in these compounds of the non-metals with hydro- 
gen, are found by actual analysis, and then they may be 
shown by their formulas, each symbol of an element 
standing for one combining weight. Let us take one 
formula from each of the four groups which we have 
studied, as an example, — 

HC1 H 2 H 3 N H 4 C 

and we see that one combining weight of chlorine combines 
with one of hydrogen, but that one of oxygen is not sat- 
isfied with so little ; it must have two. One combining 
weight of nitrogen refuses to unite with less than three of 
hydrogen, while one of carbon demands four. 

But we may as well say atoms, as combining weights, 
for, by the atomic theory, a combining weight of an ele- 
ment represents one atom. If so, the formulas show that 
one atom of chlorine can hold one atom of hydrogen, 
that an atom of oxygen is able to hold two, while an 
atom of nitrogen is able to hold three, and an atom of 
carbon, still more powerful, is able to hold four. In this 
way it appears that these atoms differ in their power to 
hold atoms of hydrogen in combination in a molecule. 

188 



VALENCE. 189 

Valence. — Now this power of an atom to hold a defi- 
nite number of other atoms in a molecule is called its 
valence, 1 

The valence of an atom is measured by the number of 
hydrogen atoms which it can hold in combination. Thus 
the valence of chlorine is 1, of oxygen is 2, of nitrogen 
is 3, and of carbon is 4. 

The valence of an atom is described by a prefix. Thus 
chlorine is said to be w/uvalent, oxygen bivalent, -nitrogen 
bivalent, and carbon quadrivalent. 

The valence of an atom is shown to the eye usually by 
primes or dashes, written with the symbol, thus : 

CI 1 or Cl_ shows that chlorine is a univalent element. 
O" " = " " oxygen " bivalent " 

N'" " Xe " " nitrogen " trivalent " 

C"" " Ce " " carbon " quadrivalent " 

The place of the dashes is of no consequence j they may 
be written above the symbol, below, at the right, or at 
the left of it. Thus : 

Cl_ —O— — N— — C— 

I 

It is the number of dashes which shows the valence of 
the element. 

Substitution is Governed by Valence. — Chlorine 
will take the place of hydrogen in methane. To bring this 
about it is only necessary to mix the two gases and put the 
mixture in diffuse light. When this is done, it is found 
that the chlorine will take the place of the hydrogen grad- 
ually, until none is left. Methane, CH 4 , may as well be 
written CHHHH. Then it is found that, — 

1 This property is also called quantivalence, and equivalence, and 
valency, by different writers. To call it valence is one of the later 
suggestions, and one worthy of general adoption. 



190 VALENCE. 

CHHH II is first changed to CHHHC1 
CHHHC1 " then " » C II H CI CI 
CHHC1C1 " " " " CHC1C1C1 

CH CI CI CI" " " " C CI CI CI CI 

Notice that the substitution of CI for H goes on grad- 
ually, atom for atom. The carbon gives one atom of hydro- 
gen for one of chlorine every time. 1 

The chlorine and hydrogen atoms have the same valence. 
Like bronze and copper pennies, they are different kinds 
of matter, but have the same value in making change. 
One atom of chlorine may be exchanged for one atom of 
hydrogen, and no more, in any chemical action. In fact, 
all univalent substances displace one another atom for 
atom. 

But a bivalent atom is worth as much as two univalent 
atoms, and, in chemical action, the exchange must be made 
one atom for two. So one quadrivalent atom is worth two 
that are bivalent, and two trivalent atoms are worth three 
that are bivalent, in all chemical changes. 

"What is the Valence of Boron? — Boron will not com- 
bine with hydrogen, but it will with chlorine. The chlo- 
ride is BC1 3 . Here we see one atom of boron holding 
three univalent atoms of chlorine, which shows that boron 
is trivalent. 

In this way the valence of many other elements has been 
found ; if they have no hydrogen compounds their chlorine 
compounds, or their compounds with some other element 
whose valence is known, may be used instead. The val- 
ence of the metals has been found in this way. 

Valence Useful in "Writing Reactions The valence 

of the elements tells us how many atoms must take part 
in a reaction, and helps one to see how many molecules of 

1 The H which is driven out combines with other atoms of CI to 
form II CI, 



VALENCE. 191 

each substance are involved in the change which goes on. 
For example : 

We have found that sodium with hydrochloric acid yields 
sodium chloride and hydrogen (Ex. 76). But sodium is 
univalent, and so we write 

Na' -hirer rrNaCl + H 

So also zinc and hydrochloric acid yield zinc chloride 
and hydrogen (Ex. 78). Shall we write 

Zn-f HC1 = ZnCl + H 

No, because zinc is bivalent ; one atom of zinc is worth 
two atoms of hydrogen, and must take the place of two. 
But there is only one in one molecule of H CI, and there- 
fore we must write 

Zn" + 2 H' CI' = Zn" Cr 2 + 2 H 

Many reactions already studied will now seem clearer in 
the light of this explanation, furnished by valence, and 
in the future study of chemical actions valence will help 
us much. 

The Valence of an Element changes But the val- 
ence of the same element is not always the same. It de- 
pends partly on the other substance with which it acts. 
Sulphur is bivalent with hydrogen, H 2 S" but it is quad- 
rivalent with oxygen S^O'V And nitrogen, a trivalent 
element, sometimes has a valence of five. Still the changes 
in valence are very regular, and they do not greatly hinder 
our using valence as a guide in writing common reactions. 



METALS. 

What is a Metal? — We think of a metal as a sub- 
stance which is heavy, hard, and lustrous, and a good 
conductor of electricity and heat, because most of the 
common metals have these properties in high degree. 

But there are some metals which are as soft as wax and 
lighter than water. In some conditions, metals are not 
at all lustrous, and some are not very good conductors. 
We must look further than to these properties for a real 
difference between metals and non-metals. It will be found 
in their chemical actions. 

The compounds of other non-metals with hydrogen and 
oxygen are acids, while the compounds of metals with 
hydrogen and oxygen are bases. Eemember that acids 
and bases are just opposite in character, and yet both 
contain hydrogen and oxygen. The other element which 
is combined with these two must be very different, in 
order to make an acid in one case and a base in another. 
And those which form the acids are the non-metals, while 
those which form the bases are the metals. 

A metal is an element whose compound with hydrogen and 
oxygen is a base. 

There is another chemical action in which metals and 
non-metals differ. Remember what has been said about 
salts, that they are made by putting another element 
into an acid in place of the hydrogen. Now, these ele- 
ments which can take the place of the hydrogen in acids 
are the same ones which, united with hydrogen and oxy- 
gen, form the bases ; they are the metals. This gives us 
another definition ; 

192 



METALS. 193 

A metal is an element which ivill take the place of hydro- 
gen in an acid and form a salt. 

Accordingly the chemist divides the seventy-one elements 
into two classes, metals and non-metals, and in a general 
way the division is right. But nature does not draw any 
such sharp line of division through the list of elements. 
There are some elements whose compounds with hydrogen 
and oxygen are sometimes bases and sometimes acids. 
This is true of iron. The fact is, that while some of the 
elements are perfect non-metals, and some are perfect 
metals, there lie, between these, others which are less and 
less perfect, and some which are almost as much one as 
the other. In nature there is a gradual difference, in the 
properties of the elements, running from one end of the 
list to the other. 

Number and Abundance of the Metals. — We have 
seen that the non-metals are included in four groups, and 
that they number only fifteen. All others of the seventy- 
one elements are metals. 

Most of this large number of metals are rare substances 
seldom seen or little used. Not more than fifteen or 
twenty are abundant in nature or useful in the arts. 

In our study of the metals we will select those which 
will teach us the most chemistry, are the most abundant, 
and the most useful. The study of the complete list of 
metals and their compounds need be attempted only by 
students who are to become chemists. To such this pres- 
ent course is simply a preparation. 

Occurrence of Metals in Nature. — There are a few 
metals which are sometimes found free in the earth, not 
pure, but simply mixed with other things. Gold and 
silver and copper are examples. Metals when found in 
this condition, uncombined with other elements, are called 
native metals. 



194 METALS. 

But the metals are usually found in combination with 
non-metals. In fact, the solid earth is made up of such 
compounds. But the rocks generally contain so much 
besides these compounds, or it is so difficult to get the 
metals out of them, that they are worthless for this pur- 
pose. 

There are, however, some parts of the rocky masses, 
which are made up of metallic compounds, so rich in metal 
that they are valuable substances from which to get the 
metals themselves. Such compounds of the metals are 
called ores. 

The work of taking these ores out of the earth is 
mining, and that of getting the metal out of the ore is 
metallurgy. Mining is a mechanical operation, and we 
will not stop to describe it, but metallurgy is a chemical 
art, and we will study it in connection with several of 
the common and the useful metals when we reach them, 
as a good example of the application of chemistry to 
useful purposes. 

The most valuable ores of the metals are the oxides, 
the sulphides, the chlorides, and the carbonates. 



THE POTASSIUM GROUP. 

POTASSIUM. K f . 

Description of the Metal — Most metals are very hard, 
but potassium is as soft as wax. It is easily moulded by 
the fingers or cut with a knife. When freshly cut, the sur- 
face shines with a blue-white luster. 

Most metals are heavy, but this one is lighter than 
water. A piece dropped on water will float like cork. 
]STor is this the only thing that will surprise one, who for 
the first time drops potassium on water; the metal will 
instantly take fire. Violet-colored flames will burst from 
it, while the melted globule will run wildly over the water, 
wasting away all the time, until, when nearly all gone, it 
will usually put a stop to the action by a small explosion. 

Its Chemical Action on Water The product of this 

action is found to be a base. (How would you prove it ?) 
It is the potassium hydroxide. We may write the reaction 

HHO + K = KHO + H 

Water Potassium 1 Potassium hydroxide Hydrogen 

The atom of potassium is univalent. It takes the place 
of one of the two atoms of hydrogen in a molecule of water, 
and forms a molecule of the hydroxide. 

Hydrogen and much heat are also set free ; in fact, heat 
enough to set the hydrogen on fire. A little of the potas- 
sium itself also burns, and it is this which gives violet color 
to the flame. 

Occurrence in Nature. — Compounds of this metal 
are present in all fertile soils, and from the soil they pass 

1 The Latin name of potassium is Kalium, and the symbol, K, is 
taken from this. 

195 



196 THE POTASSIUM GROUP. 

into the bodies of plants. In some places potassium nitrate 
is found in the earth in large quantities ; this is true of 
the dry tropical countries like Egypt and India. It is 
very soluble, and can be easily washed out by water. It 
is known in commerce as nitre or saltpetre. Potassium 
compounds are obtained for commerce either from plants 
or from the soils which contain them in large enough 
quantities. 

Potassium Carbonate. K 2 C O s . — When wood is burned 
the compounds of potassium in it are all changed to potas- 
sium carbonate, which becomes a part of the ash. To get 
it out, the ashes are washed with hot water, for it is well 
known that the carbonate is soluble, and then, to get it 
in solid form, the solution is evaporated until the car- 
bonate crystallizes out. Of course everything else in the 
ashes, which is soluble, will come out with the carbonate. 
The product is very impure ; it is called potash. 

The only chemical action in this process is the burning 
of the wood. The method of getting the potash out of 
the ashes may always be used to separate a substance 
which is soluble when it is mixed with others which are 
not. 

Many of the other useful compounds of potassium are 
made from the carbonate by chemical processes. 

Potassium Hydroxide. K H O. — Potassium will drive 
the metal calcium out of combination with hydrogen and 
oxygen, and take its place. This fact being known, the 
chemist uses it to get potassium hydroxide. 

He mixes slaked lime, Ca"H 2 2 , with potassium car- 
bonate in water, and boils the mixture. The metals simply 
change places. 

Ca"H 2 2 + K' 2 C0 3 = CaC0 3 + 2KHO 

Calcium Potassium Calcium Potassium 

with become and 

Hydroxide Carbonate Carbonate Hydroxide 



THE POTASSIUM GROUP. 197 

The calcium carbonate is a white solid which falls to 
the bottom, while the potassium hydroxide stays in solu- 
tion. This liquid is then boiled down in iron pans. 

Potassium hydroxide is the same as caustic potash. It 
has a remarkable attraction for water. It cannot be kept 
except in tight bottles, for if left in the open air it will 
take moisture enough to completely dissolve it. Some 
other things have this same property ; they dissolve in 
water which they get out of the air. Such substances are 
said to be deliquescent. 

Other Compounds made from K 2 0O 3 There are 

a great many compounds of potassium which can be made 
by starting with the K 2 C 3 . 

Ex. 126. — Make a little potassium chloride. To do this, 
first dissolve K 2 C0 3 , as much as you can, in say 50 cc. of 
water. Then add H CI slowly, until, after shaking it, the 
liquid will redden a bit of blue litmus-paper. Finally 
evaporate the liquid to a small bulk and let it cool. Pour 
the liquid away from the crystals, and dry them on filter- 
paper. Keep this potassium chloride, K CI. 

Why was the litmus-paper used ? 

What reaction took place ? 

Ex. 127. — Make some potassium nitrate in the same 
way, only use nitric instead of hydrochloric acid. If the 
evaporation is carried far enough, you can watch the crys- 
tals growing in the liquid while it cools. Keep this KaST0 3 . 

Ex. 128. — Make a little acid potassium tartrate. To do 
this first make a strong solution of K 2 C 3 in one tube or 
bottle, and a strong solution of tartaric acid in another. 
Then add the acid to the carbonate, until a piece of litmus- 
paper is reddened by the mixture. A white crystalline 
precipitate, or solid, will be made. This is the acid potas- 
sium tartrate, known in the shops as " cream of tartar." 
Keep this. 



198 



THE POTASSIUM GROUP. 



When the two liquids were put together in the last 
experiment a solid made its appearance. Any solid made 
in this way is called a precipitate. It takes the solid form 
because it is not soluble in the liquids. This, and one or 
two others, are the only precipitates which we can make 
from potassium compounds, because the acid tartrate and 
one or two others are the only potassium compounds which 
do not readily dissolve. Even these dissolve a little, and 
on this account no precipitate will come unless the solu- 
tions used are strong. 

Flame Color The flame of potassium is violet, and 

this color is seen when any compound of this metal is de- 
composed by heat. Thus : 

Ex. 129. — I take a piece of platinum-wire and bend one 
end into a round loop about as large 
as this O- I moisten this loop and 
plunge it into the K CI made in Ex. 
126. A little of the salt will cling 
to the wire, and I hold it in the 
mantle of a colorless flame (Fig. 
63), and notice the violet color of 
Fi s- 63 - the flame above. 

Look at this colored flame through a piece of cobalt-blue 
?lass. Is the violet visible ? 




Ex. ISO. — Thoroughly clean the loop so that it will not 
color the flame, and then try the K N 3 of Ex. 127 in the 
same way. 

Try also the acid tartrate of Ex. 128. 

The color will sometimes come more surely if the loop 
is moistened with hydrochloric acid. Try K 2 C 3 without 
hydrochloric acid and then with it. 

None but potassium compounds will give this color. 



THE POTASSIUM CROUP. 199 



SODIUM. Na. 

The metal sodium is so much like potassium that a 
separate description is scarcely needed. Moreover, the 
student has already seen or handled it in several experi- 
ments of this course, and can remember its appearance 
and actions. 

Sodium in Nature. — Common salt is made of sodium 
and chlorine, it is sodium chloride, Na CI. Immense quan- 
tities of this are in the seas, and large beds of it are found 
in the earth. It is also in the salt-springs which are found 
here and there. Many other compounds of sodium also 
occur, in large quantities, in the earth ; the carbonate and 
the nitrate may be mentioned. 

Sodium Carbonate. Na 2 0O 3 . — This, next to com- 
mon salt, is the most important compound of the metal. 
It may be made from the ashes of sea-plants, just as 
K 2 C 3 is made from the ashes of land-plants, but enough 
of it could not be had from this source, for it is used in 
making glass, and soap, and in other large industries. 

For these uses it is made from common salt. About 
half a ton of salt is heated in a furnace with sulphuric 
acid. This changes the salt into sodium sulphate and sets 
hydrochloric acid free. Thus : 

H 2 S0 4 + 2Ts T aCl = Na 2 S0 4 + 2HC1 

Then this sulphate, Na 2 S0 4 , also called " salt-cake, " 
is mixed with coal and fragments of limestone, and heated 
intensely until the whole is melted. 

The sulphate is decomposed by the carbon, which seizes 
its oxygen and flies away as carbon monoxide gas, while 
sodium sulphide is left behind. Thus : 

Na 2 S0 4 + 4C = Na 2 S + 4CO 



200 THE POTASSIUM GROUP. 

The sodium sulphide, ]STa 2 S, and the limestone, CaC0 3 , 
then attack and decompose each other, — 

Na 2 S + CaC0 3 = Na 2 C0 3 + CaS 

and a mixture of sodium carbonate and calcium sulphide, 
Na 2 C 3 and Ca S, called " black-ash/' is left. 

The carbonate is then dissolved out of the black-ash 
by water, after which, by evaporating the water, the car- 
bonate comes out as crystals. The sodium carbonate made 
in this way is known in commerce as soda-ash. 

There is another carbonate of soda which is made by 
running carbon dioxide through a solution of Na^CCV it 
is the acid carbonate, NaHC0 3 . This is "baking-soda." 1 
It is much used in "baking-powders," and to furnish the 
carbon dioxide gas for making "soda-water." 

Sodium Hydroxide. NaHO. — This substance is so 
much like potassium hydroxide that either may be used 
for the same purposes in the laboratory and in the arts. 
Both are used in soap-making. They combine with the 
acids which are in fats and oils, and the salts which are 
thus made are called soaps. There is this difference, 
however: the potassium hydroxide makes the soft soaps, 
while the sodium hydroxide yields the hard soaps. 

The "caustic soda," or sodium hydroxide, is made from 
Na 2 C0 3 in the same way (how?) that "caustic potash" is 
made from K 2 C 3 . 

The compounds of sodium are all quite freely soluble 
in water. (Can a precipitate be obtained from a solution 
of any of them by tartaric acid, as in Ex. 128?) 

1 In the exercises, pp. 39 and 40, the student must have come to 
the conclusion that " baking-soda " is a sodium carbonate. Having 
now gathered more facts, he finds that his conclusion was true, but that 
it was not the whole truth. Wholly reliable conclusions can never be 
reached until " the facts are all in." 



THE POTASSIUM GROUP. 201 

Flame Color. — The flame of sodium is pure yellow, 
and any of its compounds decomposed, by heat, will yield 
this color intensely. Thus : 

Ex. 131. — Wash the platinum loop and hold it in the 
Bunsen flame. Is not the flame tinged yellow? Wash 
the wire, and burn it repeatedly until it does not give the 
yellow tint, and then use any sodium compound. Note 
the rich color it imparts. 

Look at this colored flame through cobalt-blue glass : 
is the yellow color to be seen ? 

There is a little sodium in the air, in the dust of the 
room, and almost everywhere. The yellow tint of sodium 
may be given by this small quantity that is ever present. 
Only a deep, rich yellow can be trusted to show the pres- 
ence of a sodium salt in quantity. 

Ex. 132. — Make a mixture of a sodium and a potassium 
salt and burn the mixture on the platinum loop. 

Which color, yellow or violet, can you get with the 
naked eye ? 

Which, if you look through cobalt glass ? 

Ex. 133. — Make a strong solution of some of the mix- 
ture, and then add a little tartaric acid. Does a precipi- 
tate form in the liquid ? Is this precipitate made by the 
potassium or the sodium salt ? What is it ? 

AMMONIUM (?) NH 4 . 

We have seen that from ammonia, NH 3 , we may get 
a class of salts called the ammonium salts. Is there a 
metal in these salts ? 

Some Facts Ammonia, NH 3 , is very soluble in 

water (Ex. 56), and this solution will restore reddened 
litmus to blue, and it also neutralizes acids. This shows 



202 THE POTASSIUM GROUP. 

that it is a base, and yet it is made up of nothing but 
nitrogen, hydrogen, and oxygen, — all non-metals, — 

N H 3 + H 2 O = N H 4 H O. 

Ammonia combines with hydrochloric acid (Ex. 9), to 
make what is called ammonium chloride. This is a white 
solid, which has all the properties of a salt, resembling the 
chlorides of sodium and potassium, and yet it is made up 
of nothing but nitrogen, hydrogen and chlorine, — all non- 
metals. 

Ammonia solution neutralizes nitric acid and forms am- 
monium nitrate (Ex. 59), and this is as much a salt as 
is any other nitrate, but yet it is made of only nitrogen, 
hydrogen, and oxygen, — all non-metals. We find no metal 
in these ammonium compounds. 

Comparison of Formulas. — Let us now compare these 
compounds with those which do contain a metal, — say the 
metal potassium. 

Potassium hydrate, KHO, and Ammonium hydrate, NH 4 HO 
Potassium chloride, K CI, and Ammonium chloride, X II 4 CI 
Potassium nitrate, K N 3 , and Ammonium nitrate, NH 4 ^0 3 

Notice that instead of K in the potassium compounds 
we find ]STH 4 in the ammonium compounds. The ]SrH 4 
acts just like the metal potassium in making salts, and 
this leads us to say that N H 4 may be a metal also. 

A Hypothetical Metal. — But we cannot get the N H 4 
separate, as a metal. These atoms hang together well 
while in the salts, and in reactions, but part at once if 
driven out together. In chemical changes the group acts 
as if it were a metal, and we may suppose it to be one. 
We call it ammonium, and may give it a symbol, Am. 

Its Salts. — The ammonium salts are numerous. Am- 
monium chloride, Am CI, Ammonium carbonate, Am 2 C0 3 , 






THE POTASSIUM GROUP. 203 

and ammonium sulphide, Am 2 S, may be mentioned. The 
source of these salts in commerce has been already given, 
and should now be recalled by the student, p. 85. 

The Sulphides. — Only the sulphides need a word more. 
There is more than one ammonium sulphide, but they are 
all made by dissolving hydrogen sulphide gas in ammonia 
water. Large volumes of gas will be absorbed. Thus: 

H 2 8 + NH 3 = N H 4 H S, — Ammonium hydrosulphide. 

But if ammonia is also present with this NH 4 HS, they 
combine. Thus : 

N" H 4 H S + N PI 3 = (N H 4 ) 2 S, — Ammonium sulphide. 

The solution of these two sulphides is colorless, but if 
any free sulphur is in it, the liquid becomes yellow. The 
sulphur unites with the sulphide. Thus: 

(N II 4 ) 2 S + S = (N" H 4 ) 2 S 2 , — Ammonium disulphide. 

This last-named sulphide is yellow. 

The ammonium sulphide solution is one of the most 
useful reagents, as the student will soon find. But this re- 
agent, called ammonium sulphide, is not a single compound ; 
it is a mixture of all these. We may study the ammonium 
compounds further, and compare them with potassium and 
sodium, as follows : 

Ex. lSIf. — Add some tartaric acid solution to a strong 
solution of any ammonium salt. 

Note whether a precipitate comes as with potassium. 

Ex. 135. — Find out whether an ammonium salt will 
give any particular flame-color. 

Ex. 136. — Mix a little solid or liquid ammonium salt, 
of some kind, with a little K H 0, and gently heat it in a 
test-tube. 

Notice the odor ; what substance is set free ? 



204 THE POTASSIUM GROUP. 

Ex. 137. — Place a little solid ammonium salt in a por- 
celain dish, and gradually heat it. 

Does it melt ? What change does occur ? 

The Facts. — Tartaric acid gives a white precipitate in 
strong solutions of ammonium salts, because the acid tar- 
trate of ammonium is not very soluble. But the ammo- 
nium salts generally are very soluble, and on this account 
they need not be expected to give precipitates. They give 
no color to the flame. They are decomposed when heated 
with caustic potash, and then yield ammonia gas, known 
by its odor. Heat alone drives them into vapor completely, 
leaving nothing behind. 

The change of a solid directly to vapor, without first 
melting, is called sublimation. Camphor is the most fa- 
miliar example of substances which sublime when heated. 
The ammonium salts, as a class, do this. 

THE POTASSIUM GROUP. 

Potassium, sodium, and ammonium (?) are very much 
alike, and besides these there are three other metals, 
whose salts are less common and useful, also like these 
in chemical character. They are lithium, caesium, and 
rubidium. These six form a single family of metals, 
generally called the Metals of the Alkalies. 

These elements are all soft, light, and silvery white. 
They lose their luster at once in air, because they have 
so strong attraction for oxygen that the surface is tar- 
nished with oxide. They cannot, therefore, be kept in air, 
but must be put up in naphtha, a liquid which has no 
oxygen in it. They decompose water whenever they touch 
it, and form bases by the action. 

These are the most powerful bases known, — the most 
caustic and .the most ready to neutralize acids. They 



THE POTASSIUM GROUP. 205 

form the same classes of salts, and these salts are much 
alike in properties. These metals are all univalent. 

Query. — By what experiments would you mid out whether 
a given salt is a potassium, a sodium, or an ammonium com- 
pound ? 

Application. — Take from the teacher, or a friend who knows 
what they are, some substances, and see if you can decide 
whether each is a potassium, or a sodium, or an ammonium com- 
pound. 



THE CALCIUM GROUP. 

CALCIUM. Ca". 

The metal calcium is about as hard as gold, and shines 
with a yellow luster. It tarnishes quickly in air. Xo 
use has ever been made of the element itself, but its 
compounds are not only very useful, but very abundant. 

Occurrence in Nature. — Calcium carbonate, Ca"C0 3 , 
is one of the largest constituents of the earth. Marble is 
its purest natural form, but limestone is chiefly the same 
thing, and the limestone rocks make up a large part of 
the earth's crust. Calcium carbonate is the starting-point 
in the manufacture of the useful salts of this metal. 

The Effect of Heat on the Carbonate When a piece 

of marble is heated intensely, it will not be much changed 
in looks ; its size will be the same, its color somewhat 
whiter. But it will be found to be more easily crushed, 
and it is easily shown that a chemical change has occurred. 
This may be done by treating it with water. Very soon 
after being wetted, the stone begins to swell and crack and 
crumble, while volumes of steam arise, and when all is over 
a fine white powder remains. 

The fact is, that heat decomposes the marble, and drives 
off carbon dioxide. Thus : 

CaC0 3 + heat = CaO + C 2 

and the white mass left behind is the calcium oxide, Ca 0. 
The common name of this oxide is quick-lime. 

By this simple chemical process large quantities of 
quick-lime are manufactured. The furnaces are called 
lime-kilns. 

206 






THE CALCIUM GROUP. 207 

The white powder made by the action of water on 
quick-lime is called slaked-lime. The water actually com- 
bines with the oxide. Thus : 

CaO + H 2 = CaH 2 2 + heat 

We see by the formula that slaked lime is calcium 
hydroxide. The heat of this chemical action is remarkable. 

Among many uses of slaked-lime, we may mention that 
of making mortar for building purposes. Mortar is made 
by mixing slaked-lime and sand, and it is used to cement 
together the bricks or stones in the walls of buildings. 
Fresh mortar is very weak; it becomes a strong cement 
after it is laid up in thfe walls. The chemistry of the 
change is this : 

Calcium hydroxide absorbs the carbon dioxide of the air, 
when exposed, and is slowly changed by it into calcium 
carbonate, which is hard and stony, and this, filled in with 
grains of sand, becomes a strong and solid mass which 
cements the bricks or stones together. 

The calcium hydroxide, CaH 2 2 , is slightly soluble in 
water: the solution is known as lime-water, and is very 
useful to the chemist (Exs. 6, 26, 73), and to some extent 
in medicine. 

Effect of Acids on the Carbonate Even the weaker 

acids will decompose marble, and in fact most other car- 
bonates. Water and carbon dioxide are produced by this 
action and the escape of this last in bubbles is the effer- 
vescence which always occurs. Turn back, now, to the 
preparation of carbon dioxide (Ex. 73). We wanted the 
C0 2 then, and did not take account of anything else. But 
we can now see what the complete reaction really was. 
Thus : — 

Ca"CO, + 2HC1 became CaCL + H 2 + C0 2 



208 THE CALCIUM GROUP. 

and this illustrates the action of other acids on this sub- 
stance. Carbon dioxide, water, and a salt of calcium are 
the products. 

Effect of Water on the Carbonate. — Pure water will 
not dissolve this carbonate, but water holding C 2 in 
solution dissolves it quite readily. Let the C 2 escape, 
or drive it out by heat, and the carbonate reappears. 

This action goes on in nature. Rain-water contains 
C 2 , taken from the air, and as this water runs over the 
lime-rocks it dissolves and carries some of their substance 
along. But when this solution is exposed to air, the G 2 
escapes, and the water then drops the solid carbonate. 
This occurs in caverns where the water trickles through 
their roofs. Each drop leaves a little solid carbonate 
behind when it falls, and an icicle-like mass slowly grows 
from the roof. This is called a stalactite. Another grows 
up from the floor, this is called a stalagmite. 

The Sulphate. CaS0 4 4- 2H 2 0. — This is known as 
gypsum, — a crystalline mineral found in some abundance, 
and, when ground to powder, quite useful as a fertilizer. 
This mineral gives up its water, 2 H 2 0, when strongly 
heated, and crumbles to a fine white powder called "Plas- 
ter of Paris" Wet this plaster of Paris, and it combines 
with water again and hardens into stone. This curious 
property makes the sulphate useful for making casts. 

Glass contains calcium silicate, combined with silicates 
of sodium or potassium (see p. 185), and bleaching powder is 
a mixture of calcium hypochlorite and calcium chloride. 
How is it prepared ? See p. 141, and Ex. 86. 

To Prepare the Insoluble Compounds. — Among the 
many salts of calcium there are several that are not solu- 
ble in water, especially in water that contains ammonia, 
and such can be obtained by precipitation. 

Ex. 138. — Place about 5 cc. of calcium chloride in a test- 



THE CALCIUM GROUP. 209 

tube, add about as much water, and heat the mixture up to 
boiling-point. Then add slowly a solution of ammonium 
carbonate as long as it continues to produce the precipitate. 
The time to stop may be known by letting the solid settle 
a little, and then notice whether another drop of the ammo- 
nium carbonate has any effect. The white precipitate is 
calcium carbonate. Am CI was also made, but stays dis- 
solved in the clear liquid. Thus : 

CaCl 2 -f (i\H 4 ) 2 C0 8 = CaC0 3 + 2NH 4 C1 

A very valuable fact is shown in this experiment. Xotice 
that one carbonate precipitates another. We wanted to 
make the insoluble CaC0 3 , and we did it by using the sol- 
uble (NH 4 ) 2 C0 3 . The fact is, that a soluble salt precipi- 
tates an insoluble salt of the same class as itself. If we 
want an insoluble hydrate we will use some soluble hydrate 
to make it. Or, if we want an insoluble sulphide we will 
use some soluble sulphide to produce it. There are a few 
exceptions to this rule, but it is so generally true as to 
be an excellent guide. 

For example, we wish to make the insoluble calcium 
sulphate. Let us select some soluble sulphate to do it 
with. It may be potassium sulphate, K 2 S0 4 , or hydrogen 
sulphate, H 2 S0 4 , or some other. 

Ex. 1S9. — Place about 5 cc. of water in a test-tube, and 
add about as much solution of any soluble compound of 
calcium, — such as the chloride or nitrate, — and then add, 
little by little, a solution of K 2 S 4 . 

Repeat the operation, using H 2 S 4 . 

The precipitate is calcium sulphate in both cases. 

Can you write the reactions ? 

But the term insoluble is not applied to a substance, 
because the fluid dissolves absolutely none of it; we call 
a thing insoluble when a fluid dissolves only very little, 



210 THE CALCIUM GROUP. 

Everything is soluble in some degree, but in many cases 
the quantity, which will dissolve in the amount of fluid 
used, is too small to be taken account of. Such are called 
insoluble substances. 

Now CaS0 4 is somewhat soluble in water. In fact, 
400 cc. of water will dissolve about 1 g. of it, and if you 
have, say 10 cc. of fluid in your test-tube (Ex. 139), there 
must be about £ G of a gram of the sulphate in solution ; 
the rest of the sulphate is the precipitate. A precipitate 
will always be seen whenever the fluid present cannot 
dissolve all of the substance which the reagent makes, 
but not otherwise. 

To Prepare Soluble Compounds If ? in any case, 

the new compound made by a chemical reagent is soluble, 
it may be obtained by evaporating the clear liquid, in 
which it is dissolved, until crystals will form, or to dry- 
ness if necessary. For practice, the student should pre- 
pare some calcium nitrate, and calcium acetate, from the 
pure carbonate, or from marble. 

THE CALCIUM GROUP. 

Two other metals, barium, Ba", and strontium, Sr", are 
very much like calcium, and these three form the calcium 
group of metals, or, as it is also called, the group of the 
alkaline earths. 

In general, these three metals combine with the same 
substances and in the same proportions. Their attraction 
for oxygen makes them tarnish quickly in air, and en- 
ables them to decompose water when they touch it. The 
hydroxides thus formed are strongly alkaline. In these 
chemical actions barium is more energetic than strontium, 
and strontium more than calcium. Xow this is also the 
order of their atomic weights, if we start with the largest. 

Thus: 

Ba = 137 Sr = 87.5 Ca = 40 



THE CALCIUM GROUP. 211 

This is another illustration of the curious fact, noticed 
among groups of the non-metals, that the properties of 
elements seem to depend on their atomic weights. 

The great resemblance of barium and strontium to cal- 
cium will be seen if we make and compare some salts of 
these three metals. Some differences will also be dis- 
covered. 

Ex. lJfO. — Make the carbonates of barium and strontium 
just as that of calcium was made in Ex. 138, and notice 
how much alike these three carbonates appear. 

Ex. HI. — Arrange three test-tubes, each with 5 cc. of 
water, and add to one 5 cc. of strong solution of Ba Cl 2 , to 
the second, as much strong solution of SrCl 2? and to the 
third, as much strong solution of CaCl 2 . Then add to each 
a little solution of calcium sulphate. 

Notice a precipitate at once in the Ba tube only. Heat 
the other two to boiling, and notice then a precipitate in 
the Sr tube, but none in the other. 

The barium sulphate forms at once in the cold. 

The strontium sulphate at once only when heated. 

The calcium sulphate does not form at all. 

This experiment will help us to decide, in any case, 
which one of these three metals, if either, is present in a 
given solution. But why is not the calcium sulphate pre- 
cipitated here as it was in experiment 139 ? 

Flame Colors. Ex. 1J+2. — A volatile compound of cal- 
cium will tinge the flame yellow-red ; of strontium, brilliant 
crimson ; of barium, green. Try these compounds, and ob- 
serve the flames with the naked eye, and also through cobalt 
glass. Mark well the difference between these and the 
flame colors of potassium and sodium. 



METAES OF THE ZIXC GROUP. 

Magnesium. Mg". — The metal magnesium is found 
as a carbonate and as a silicate, these two being its most 
important compounds in the rocks. Its sulphate, known 
as Epsom salt, is its most important compound. It is 
found in solution, and in some mineral springs it is a val- 
uable constituent. What is commonly called magnesia is 
the oxide of this metal, Mg"0. It is used in medicine. 
The Epsom salt, Mg S 4 + 7 H 2 0, is still more valuable 
as a medicine ; but on the whole magnesium and its com- 
pounds do not rank high among useful substances. 

The chemical actions of magnesium compounds are a 
little like those of the calcium group. Its carbonate is 
insoluble in water. 

Ex. 143. — Precipitate Mg"C0 2 from its chloride just 
as was done for CaC0 3 in Ex. 138. 

Ex. I44. — Put 5 cc. ammonium chloride in a test-tube, 
and to this add 5 cc. of magnesium chloride. Then add 
the ammonium carbonate. Does a precipitate form ? If 
not it shows that magnesium carbonate is soluble in 
ammonium chloride. This is a fact. In this respect this 
carbonate differs from those of the calcium group. In 
general the compounds of this metal are more soluble than 
those of that group. 

ZINC. Zn". 

The metal zinc is found in several minerals which occur 

in considerable quantities in the rocks, such as " calamine," 

which is the carbonate, "blende," which is the sulphide, 

and "zincite", the oxide. These are its most valuable ores, 
212 



METALS OF THE ZINC GROUP. 213 

Zinc is a useful metal, and it is manufactured on a large 
scale from these native compounds. 

Manufacture of Zinc Suppose the metal is to be 

taken out of the oxide, Zn 0. The problem is how to get 
rid of the oxygen. Turn back to Ex. 72, and you recall 
the strong attraction of carbon for oxygen, and how, on this 
account, carbon reduced Cu to metallic copper. Now this 
is the fact applied to get the zinc out of Zn on a large 
scale. The oxide and charcoal are put into vessels of fire- 
clay and heated in a furnace. What reaction occurs ? It 
may be written : 

Zn O + C = C O + Zn. 

The zinc, in the form of vapor, is led out into cold 
vessels, where it is condensed. 

But suppose the zinc is to be taken out of one of the 
other ores, — say the sulphide, Zn S. The problem, then, is 
to get rid of the sulphur. The problem is solved by first 
changing the sulphide into the oxide, and then reducing 
the oxide by carbon as before. And to change the sul- 
phide to oxide it is simply heated in the air, when oxygen 
of the air takes the place of sulphur in the ore. Thus : 

Zn S + 3 O = Zn O + S 2 

This heating of an ore in the air is called roasting. The 
object of it is to change the ore to an oxide. It is in many 
cases, as in this one, the first step in the process of get- 
ting a metal from its ores. 

Uses of Zinc. — The uses of zinc are quite numerous. 
When heated to a temperature above that of boiling water 
(125° -150°) it can be rolled out into thin sheets. This 
sheet-zinc is in familiar use. Zinc is brittle, and cannot 
be rolled out at temperatures much higher or lower than 
those given above. Zinc is also used as a covering for 



214 METALS OF THE ZINC GROUP. 

sheet-iron; for this purpose sheets of iron are simply 
dipped in melted zinc; it is then called galvanized iron. 
Zinc and copper melted together form brass. Zinc, cop- 
per, and nickel, melted together, form German silver. 
Substances like these, which consist of two or more 
metals together, are called alloys. These and other alloys 
of zinc are useful. 

Compounds of Zinc. — Of the compounds of zinc we 
may mention the following: zinc oxide, which is used as 
a paint under the name of zinc tvhite, and is made for this 
purpose by heating the carbonate. Zinc chloride, used by 
tinners for cleaning the surface of metals for soldering, 
and also as a disinfectant. Zinc sulphate, known as white 
vitriol, a poisonous substance, but used in small quantities 
in medicine. 

Preparation of Insoluble Compounds. — Among its 
compounds which are insoluble in water are the carbon- 
ate, the sulphide, and the hydroxide. To make these we 
may start with zinc chloride. 

Ex. 145. — Make a solution of zinc chloride for use, by 
putting bits of zinc in a bottle and pouring a few cubic cen- 
timeters of H CI on them. There should be zinc left in 
the bottle when the action is over, for then the zinc chlo- 
ride will be free from acid. 

Ex. 146. — Add a few drops of this solution of ZnCl 2 
to 10 cc. of water, and then add (N H 4 ) 2 C 3 . 
Describe the result and write the reaction. 

Ex. 147. To 10 cc. of water, with a few drops of Zn Cl 2 
add AmgS. 1 What is the white precipitate which falls? 

1 This ammonium sulphide, and the hydrogen sulphide for the next 
experiment, are made by passing H 2 S through dilute ammonia (half 
water) for one and water for the other. Use the same apparatus as 
in Ex. 107. 



METALS OF THE ZINC GROUP. 215 

Write the reaction. What soluble compound is also 
made in this reaction? 

Ex. US. To a few cubic centimeters of Zn Cl 2 add a few 

drops of hydrochloric acid, and then add a solution of 
hydrogen sulphide, H 2 S. Do you get a precipitate? If 
not, it shows that Zn S is soluble in this liquid. 

We make the sulphide whether we use Am 2 S or H 2 S, 
but the first is an alkaline substance, while the second is 
an acid, and Ave find that the sulphide is not soluble in 
the alkaline liquid, Ex. 147, while it is soluble in the 
acid liquid, Ex. 148. 

Ex. 149. — To a few cubic centimeters of the Zn Cl 2 with 
an equal bulk of water add NH 4 HO little by little, until 
after shaking it, and then blowing the air out of the tube, 
the strong odor of ammonia remains. 

Describe the two changes which occurred. 

The explanation is this : Ammonium hydroxide changes 
the zinc chloride to zinc hydroxide, which takes the form 
of a white precipitate because it is insoluble in ivater. But 
it is soluble hi ammonium hydroxide, and so just as soon as 
there was added more than enough to make the precipitate, 
the excess began to dissolve that which had been made. 
Whenever, as in this case, a precipitate dissolves in the 
reagent which makes it, it is said to be soluble in excess. 

The Zinc Group. — Magnesium, zinc, and cadmium are 
the members of this group. These elements are much 
alike. They are all bluish-white metals. They have 
many of the same properties, but in different degrees. 

For example, cadmium melts at a comparatively low 
temperature, zinc at a higher ; 423° C, and magnesium at 
one still higher. Cadmium becomes a vapor at a low red 
heat, zinc if heated but little hotter, and magnesium at 
a bright red heat. They take fire in the air, cadmium 



216 METALS OF THE ZINC GROUP. 

burns less freely, zinc with a fine blue flame, and magne- 
sium with a dazzling whiteness. They decompose dilute 
acids, cadmium rather slowly, zinc more freely, and mag- 
nesium very promptly. 

This order of their properties is also the order of their 
atomic weights, beginning with the largest. Thus : 

Cd Zn Mg 

112 65 24 

Suggestion. — Compare, by experiment, the action of H 2 S, and 
of Am 2 S, on some soluble compounds of zinc, cadmium, and mag- 
nesium, and note the different results. 

Then take from the teacher or a friend, who knows what they 
are, some specimens, and see if you can decide whether each is a 
compound of either of these metals. 



THE IEON GROUP. 
MANGANESE. Mb". 

As a metal, manganese need not detain us, since it 
is rarely used in chemistry or the arts. In the form of 
the "black oxide," Mn0 2 , it is found in many parts of the 
earth. This is its chief ore, although it occurs in other 
minerals and rocks in some abundance. It unites with 
oxygen in several proportions, reminding us, in this re- 
spect, of nitrogen : there are five oxides of each. 

Salts of Manganese. — Two of these — those which 
contain least oxygen — act with acids to produce salts: 
they are basic, while one of them — that which contains 
most oxygen — acts with bases to produce salts : it is acid. 
The other two do not produce salts at all : they are neu- 
tral. The student should think of the bearing of this fact 
on our definition of metal, p. 192. 

From the basic oxide, MnO, we may get manganous 
chloride and manganous sulphate, which are the salts most 
common in the laboratory, while from the acid oxide, 
Mn 2 7 , we may get the potassium permanganate, which is a 
beautiful salt, much used in the laboratory and out of it. 
Its solution in water is intensely purple, but this fine color 
is quickly lost in presence of anything which has an affinity 
for oxygen. It parts with its oxygen so readily to other 
things, that it is a most powerful oxidizing agent. In the 
laboratory, it is used for this purpose, and out of it too ; for, 
since bad odors and putrid organic matter are destroyed by 
oxygen, the permanganate is a valuable disinfectant. 

Preparation of Some Insoluble Salts. — Among the 
insoluble salts of manganese we may mention the mangan- 

217 



218 THE IRON GROUP. 

ous carbonate, sulphide, and hydrate. A study of these 
will reveal some of the most characteristic reactions of this 
metal. 

Ex. 150. — To make the carbonate, proceed exactly as in 
Ex. 146 with zinc, using a solution of manganous sulphate 
instead of the zinc compound. 

What is the color of manganous carbonate ? 

What is the color after some time in the air ? 

To answer this last question, it is well to filter the liquid, 
and leave the precipitate on the filter. The change you 
will discover is caused by the oxygen of air, which changes 
the maiigano?^.s carbonate to the manganic hydrate. This 
change does not occur in the case of zinc. 

Ex. 151. — -To make the sulphide, proceed just as in 
Ex. 147 with zinc, using manganous sulphate, and Am 2 S. 
What is the color of the manganous sulphide ? 
Write the reaction which took place. 
What soluble compound is made at the same time ? 

Ex. 152. — Try to make the sulphide by using H 2 S. 
Proceed exactly as in Ex. 148 with zinc. 
What is the result, and why ? 

Ex. 158. — To make the hydrate, MnH 2 2 , proceed just 
as in Ex. 149 with zinc, using MnS0 4 . 

What is the color of this manganous hydrate ? 
Is it, like the zinc hydrate, soluble in excess ? 
What change happens if it is left in the air? 

The pure manganous hydrate is white, but it is changed 
by oxygen into brown manganic hydrate. 

Ex. 154- — To a few cubic centimeters of the manganous 
solution, add as much ammonium chloride, and then add 
ammonia as before. 



THE IRON GROUP 219 

Do you get the precipitate ? If not, it shows that man- 

ganous hydrate is soluble in ammonium chloride. You 

# will get none of it, if enough of this chloride is present. 

Preparation of Potassium Manganate. — The man- 

ganate is soluble in water, and of course it cannot be pre- 
cipitated. But there is another way of making salts, and 
that is by fusion, or, as it is often called, the "dry way." 

Let us mix a little " black oxide " of manganese with 
an equal weight of solid potassium hydroxide and half as 
much potassium chlorate. This mixture should be strongly 
heated. It may be done in a thin iron spoon, or the bottom 
of a broken porcelain dish. When well fused, the mass will 
turn green, and this green substance is potassium manga- 
nate, K 2 Mn0 4 . Let it cool and then put it into water, and 
you shall find that the manganate dissolves, yielding a fine 
green solution. 

Preparation of Permanganate. — If now you boil 
some of this green solution, you shall see its color change 
to a rich purple-red. The fact is, that the green manganate 
is easily oxidized, and is thus changed into the red perman- 
ganate, K 2 Mn 2 8 . This change takes place on boiling its 
solution. The curious change of color, from green to red, 
has given to the manganate the name "chameleon mineral." 
The permanganate holds its oxygen very loosely, and will 
therefore oxidize other bodies readily. By this action it 
decomposes organic matter. When added to water contain- 
ing organic matter, it becomes colorless or brown by giving 
up its oxygen. 

Nickel. Ni" Nickel is a white, hard metal, which is 

much like iron, but does not rust as easily, and on this 
account it is used as a plating on the surface of other 
metals, such as steel, copper, and brass. 

Nickel salts are generally green, but the description of 
them need not detain us. 



220 THE IRON GROUP 

Cobalt. Co". — Cobalt is more rare than nickel. It 
also is a hard, white metal, with a reddish tinge however, 
and in other qualities it is much like nickel and iron. The 
salts of cobalt are highly colored, and the color depends 
on whether they contain water. Thus cobaltous sulphate, 
when it contains water, CoS0 4 , 7H 2 0, is a beautiful red 
salt, but once drive its water off by heat, and the sulphate, 
CoS0 4 , is blue. The silicate is used to color glass; so is 
the oxide. For this purpose no substance yields a richer 
blue. The blue glass used in viewing colored flames is an 
example. 

The student should prepare some nickel and cobalt salts 
and study them by making, with them, the same experi- 
ments as have been already made with salts of zinc and 

manganese. 

IRON. Fe" or (Fe 2 ) vl . 

While manganese, nickel, and cobalt are quite rare and 
little used, iron is the most abundant and the most useful 
of metals. 

Occurrence in Nature. — Iron is found in the rocks, 
in the soil, in plants, and in the bodies of animals. There 
is no metal more widely diffused than iron. 

Native iron is sometimes found in the earth, and 
" meteoric stones," which come from space outside the 
earth, are little else than iron, with also some native nickel 
and cobalt. 

The sulphide, FeS 2 , " pyrites" is found almost every- 
where, sometimes in yellow scales, sometimes in perfect 
cubes, which are also yellow. It is so often mistaken by 
the ignorant for a precious metal, that it is called " fool's 
gold." 

The chief ores of iron are two oxides and a carbonate. 
The richest of all is the "Magnetic oxide," Fe 3 4 , which is 
so called because it is able to attract a magnet. It is very 



THE IRON GROUP. 221 

abundant in this country. There are mountains of it in 
Missouri, and vast beds of richest quality in New York. 
It is black. 

Haematite is the other oxide, Fe 2 3 . It is red or brown. 
and sometimes, in the form of beautiful crystals, its color 
is dark steel-gray. 

The carbonate, FeC0 3 , is still less rich in iron, and it is 
generally mixed with clay and other earthy matters, which 
make it poorer still. Such a carbonate is called "clay-iron 
stone." 

These ores are rarely pure ; they are largely mixed with 
sulphides and earthy matter, and the red oxide contains 
water; it is Fe 2 3 , 3H 2 0. All these facts have to be 
taken into the account in the process of extracting the iron. 

Roasting the Ores. — In working other ores than the 
best oxides, they are first roasted, p. 213. In this process 
water is driven off, sulphur is burned into sulphurous 
oxide, carbon dioxide is set free from the carbonate, and 
the iron of the whole is changed into oxide, which re- 
mains mixed with the earthy matters of the ore. 

Reducing the Oxide. — The next thing to be done is 
to decompose the oxide and liberate the iron. The power 
of hot carbon to reduce an oxide, Ex. 72, is here applied. 

The process is carried out in a blast-furnace, — a furnace 
in which the fire is driven by a blast of air. Such a fur- 
nace is pictured in Fig. 64. It may be 50 or 100 feet high, 
and at its widest place inside it may be 12 or 18 feet in 
diameter. The furnace is fed from the top, and kept full 
of fuel, crushed ore, and fragments of limestone, thrown 
in together. 

The fire is started at the bottom, and is urged to the 
greatest intensity by a blast of air driven in by the power 
of a steam-engine. 

In this intense heat the earthy parts of the ore, and the 



222 



THE IRON GROUP. 



limestone, melt together into a glassy substance, called the 
"slag." The carbon of the fuel seizes the oxygen of the 

ore and sets the iron 
free. Kept melted by 
the intense heat, the 
iron runs to the bottom 
of the furnace into a 
sort of chamber made 
to receive it, while the 
lighter slag floats on 
the surface of the melt- 
ed metal. 

In front of the fur- 
nace is a large level bed 
of sand, with one main 
furrow through its cen- 
ter, and many branch 
furrows on either side, 
as shown in the cut. 

At intervals of about 

twelve hours the fur- 

Fig - 64, nace is opened at the 

bottom for the metal to run out. It then flows down into 

the furrows of the sand-bed, where it is allowed to grow 

cold. 

The iron thus made is called cast-iron, and, in the form 
of the short bars made in the sand, it is called pig-iron. 

But besides iron this cast-iron contains carbon, silicon, 
sulphur, and phosphorus, in small quantities. These im- 
purities make the metal weak, brittle, and fusible. Never- 
theless, it is used for the manufacture of a great many 
articles where great strength is not required. 

In fact, pure iron is not found at all in commerce. The 
very purest contains a little carbon. 




THE IRON GROUP. 



223 




The Three Forms of Iron. — There are three forms 
of iron, known as cast-iron, wrought-iron, and steel. 

Wrought-iron. — This is the purest form of commercial 
iron; it is the toughest, strongest, and most malleable. It 
is made from cast- 
iron by robbing 
it of its impuri- 
ties, and this is 
done by bringing 
oxygen into con- 
tact with all parts 
of the melted 
metal. The fur- 
nace in which 
this is done is 
called a rever- 
berator]/ furnace, 
and by help of 
the cut, Fig. 65, the operation may be understood. 

The cast-iron is placed upon a large hearth, D ; the fire 
is built in a separate part of the chamber. Flame and hot 
gases from the fire strike against the arched roof of the 
furnace, and the intense heat is thrown from the roof down 
upon the cast-iron. In a little time the iron begins to 
soften, and at length it becomes a pasty mass of half- 
melted metal. Then the furnace-man unstops a hole, I?, 
thrusts a paddle through it into the pasty mass, and work- 
ing this paddle about (puddling) he thoroughly stirs the 
metal, so that all parts of it are slowly brought in contact 
with the hot air at the surface. 

The hot oxygen of the air seizes the impurities, one 
after another. Some of the new compounds form a 
liquid slag, which is drawn off out of the furnace at b, 
while others are gases which pass up and out of the high 
chimney. 



Fig. 65. 



224 THE IRON GROUP. 

The result is, that the iron is soon left almost free from 
its impurities. A large part of its carbon has been burned 
away, and has gone off as carbon dioxide. A large part 
of the other impurities are also burned, but some of the 
slag, thus made, is still mixed with the purified iron. 

The furnace-man then lifts out a ball of this pasty iron, 
weighing perhaps sixty pounds, or even more, and puts it 
under the heavy blows of an immense hammer, or some- 
times under the tremendous pressure of the squeezer. In 
this way the impurities which are still mixed with the 
iron are pounded or squeezed out, so that the iron is left 
more pure and compact. 

The mass of iron is then forced through grooves between 
two strong rollers. The very great pressure of these 
rollers lengthens the mass out into a slender rod or bar. 

For the best quality of bar-iron, as this form is often 
called, the bars, made by the first rolling, are cut into 
short lengths and bound together in bundles, to be heated 
over again and rolled into bars a second time. By re- 
peating these efforts the purest and strongest iron to 
be found in commerce is obtained. It is wrought-iron, 
also called malleable iron. 

Steel. — Neither cast-iron nor wrought-iron has the 
qualities which render iron useful in all the various ways 
in which this metal is employed ; a third form, which is 
better than either of these for many uses, is steel. 

The difference between steel and the other two kinds of 
iron is best shown by the action of fire and water. 

Let wrought-iron be strongly heated and then suddenly 
cooled by a plunge into cold water. Very little if any 
change will be produced. 

Let steel be treated in the same way, and it will be made 
almost as hard as diamond, and so brittle that it will snap 
before it will bend. Let this brittle steel be heated again 



THE IRON GROUP. 225 

to a point below red-heat and then cooled, and it is softened 
somewhat, and, what is more remarkable, it is made so 
elastic that it will bend rather than break, and spring- 
back again when released from the force. 

Cast-iron may be hardened as much as steel may be, but 
it cannot be made elastic. 

With this difference in properties we find a difference 
in composition, for while each is composed of iron and 
carbon, it is found that cast-iron contains the largest pro- 
portion of carbon, wrong ht-ir on the smallest, and steel a 
proportion between the other two. 

It would seem, then, that steel could be made in two 
ways : 

By taking away some carbon from cast-iron. 

By adding some carbon to wrought-iron. And, in fact, 
the steel so largely used in the arts, is made in both these 
ways. Thus : 

1. From two to six tons of cast-iron is melted and 
then run into a large globe-shaped vessel made of a sub- 
stance which will not melt at the highest heat to be 
attained. In the bottom of this vessel there are many 
holes, and a strong blast of air is driven through them. 
The air bubbles up through the melted metal, and a most 
furious burning begins. The oxygen attacks the silicon, 
and the sulphur, and the carbon, and some of the iron also, 
and burns them into compounds with itself. 

In this way the iron is partly purified, but the chemical 
action goes too far, and removes so much carbon that too 
little is left. By adding some cast-iron to the purified 
mass, enough carbon is given back to change the whole into 
steel. 

The globe-shaped vessel (converter) is then turned on its 
pivots, and the melted steel is run out into a ladle, and 
then poured into moulds. 



226 THE IRON GROUP. 

Less than half an hour is time enough to change these 
tons of cast-iron into steel. The process is called the 
Bessemer process. 

2. In the other way of making steel, bars of wrought- 
lron are packed in charcoal, and the two are shut up to- 
gether in air-tight boxes. They are then made red-hot, and 
are kept so for several days. 

During this heating, carbon finds its way into the solid 
iron and changes the whole mass to steel. This product 
is known as blistered steel, because the bars, on coining out 
of their hot bed, are found to have a great many bubbles 
or blisters on their surface. The steel is then melted and 
run into moulds. This method of making steel is called 
cementation. 

Compounds of Iron. — Some facts about the chemical 
action of iron have been noticed already. The production 
of ferrous sulphate in Ex. 120, and of ferrous chloride in 
Ex. 94, showed the action of iron on acids, — the most direct 
way of making some salts of this metal. 

Experiments 96 and 97 are still more instructive. They 
should now be studied over again, because they prove that 
there are two distinct chlorides of iron, — the ferrous chlo- 
ride, FeCl 2 , and the ferric chloride, Ee 2 Cl 6 . And this 
illustrates a most important fact, for iron forms not only 
two chlorides, but also two sulphates, two nitrates, and, 
in fact, two large classes of salts, — the f emotes salts, such 
as ferrous chloride, and the ferric salts, such as ferric 
chloride. 

Compare the Ferrous and Ferric Compounds. — These 
two classes of iron compounds are unlike in appearance, 
and quite different in their chemical behavior. These 
differences are most distinctly shown by experiments. In 
the first place 

Ex. 155. — Make some ferrous and some ferric chloride, 



THE IRON GROUP 227 

to be used in the work which follows. To do this use clip- 
pings of small iron wire, or small nails, and add them to 
hydrochloric acid and aqua regia until these liquids will dis- 
solve no more. For directions, see Ex. 96 and Ex. 97. The 
hydrochloric acid yields solution of ferrous chloride. The 
aqua regia yields solution of ferric chloride. 

Note the colors of these solutions. 

Ferrous salts are generally light green; while ferric 
salts are generally reddish yellow or brown. 

Ex. 156. — Prepare two test-tubes, each with about 10 cc. 
of water, and add to one, 1 cc. of the ferrous chloride and 
to the other, 1 cc. of the ferric chloride. Now add ammo- 
nium hydroxide in drops to the first, and notice the precipi- 
tate which forms. Afterward treat the second in the same 
way. The ferrous chloride yields ferrous hydroxide, 
Fe(HO) 2 . The ferric chloride yields ferric hydroxide, 
Fe 2 (HO) 6 . The color of the first is light green, of the 
second brownish red. 

Now filter the ferrous precipitate out, and leave it on the 
paper in the air. You will find it turning red like the 
other hydroxide. In fact, the moist ferrous hydroxide 
actually changes into the ferric hydroxide. Thus : 

2Fe(HO) 2 + H 2 0-fO = Fe 2 (HO) 6 . 

So it is also with other iron compounds of the ous class : 
the air oxidizes them into the ic form. This illustrates 
the rusting of iron in moist air : this same reddish hy- 
droxide is made. We then call it iron-rust. 

But the ous compounds become ic compounds by the 
action of other oxidizing agents than air, — such as nitric 
acid. Thus : 

Ex. 157. — Put about 1 cc. of ferrous chloride with about 
5 cc. of water in a tube, add 4 or 5 drops of strong H N 3 , 
and then boil it gently for a minute. 



228 THE IRON GROUP. 

Notice a change in the color of the solution. 

What change in the substance does this color suggest ? 

Now add ammonium hydroxide, and observe the precipi- 
tate. Is it green or red, — ferrous or ferric hydroxide ? 

What change does this prove that the H N 3 made ? 

The nitric acid will, in the same way, change other ous 
iron compounds into the ic form. It is said to oxidize them, 
and yet it does not change them into oxides. It changed 
the Fe Cl 2 into the Fe 2 Cl 6 , and it would change Fe S 4 into 
Fe 2 (S 4 ) 3 . Whatever changes any compound from a lower 
to a higher form of combination is called an oxidizing agent. 

Ex. 158. — Put two or three drops of ferrous chloride 
with about 5 cc. of water, and then add drops of a solution 
of potassium ferrocyanide. 

In another tube make the same experiment with ferric 
chloride. Note the different results carefully. 

A beautiful deep blue precipitate is always made by 
potassium ferrocyanide in ferric salts : it is " Prussian 
blue/' The same reagent in ferrous salts yields a pale blue 
precipitate, and this difference is so marked, that one can, 
in this way, tell whether a given iron solution holds a 
ferrous or a ferric salt. 

Compare some Compounds of Iron with those of 
Zinc and Manganese. Ex. 159. — Put a few drops of 
ferric chloride in water, and add ammonium hydroxide " in 
excess/' to see whether ferric hydroxide is soluble in 
excess, like that of zinc, Ex. 149. 

Ex. 160. — Put a few drops of ferric chloride into a little 
water, add considerable ammonium chloride, and then the 
ammonium hydroxide, to see whether the ferric hydroxide 
is soluble in Am CI, like that of manganese, Ex. 154. 

Ex. 161. — To 10 cc. of water with 1 cc. of ferric chloride 
add a few drops of ammonium sulphide, Am 2 S. 



THE IRON GROUP. 229 

What is the name and the color of this precipitate ? 
Compare it with the sulphides of zinc and manganese. 

Ex. 162. — To 1 cc. of ferric chloride add a drop or two 
of hydrochloric acid, and then add a solution of hydrogen 
sulphide. Does the color of this result agree with that of 
any of the iron compounds seen before ? 

Ferrous sulphide, Fe S, is a black substance which is 
not soluble in alkaline liquids, but is soluble in acids. For 
this reason it is made by Am 2 S, but not by H 2 S. In this 
respect it is like the sulphides of zinc and manganese. The 
whiteness of the liquid in Ex. 162 is due to sulphur. The 
H 2 S is decomposed by the ferric chloride, and its sulphur 
is set free. 

Chromium. Cr. — Chromium may be made by heating 
its chloride with potassium, it is then a dark gray powder, 
which in air takes fire before it reaches a red heat. But if 
the chloride is heated with sodium, instead of potassium, 
the chromium is set free as hard and shining crystals. 
While, if the metal is made from its oxide, by heating 
it with charcoal, it has a steel-gray luster, is hard enough 
to cut glass, and combines with oxygen slowly when heated 
in the air. It is a curious fact that, if we make the same 
substance in different ways, it sometimes comes out with 
different properties, as in this case of chromium. 

In its chemical actions, chromium is sometimes a metal 
and sometimes not. With acids it forms salts, like other 
metals, such as chromium sulphate, Cr 2 (S0 4 ) 3 . But with 
bases it forms salts, like the non-metals, such as potassium 
chromate, K 2 Cr0 4 . Is it nature, or only the chemist, 
who divides the elements into metals and non-metals ? 

The chief ore of this metal is chromite, a compound of 
iron chromium and oxygen. It is not the metal itself 
which is obtained from this chromic iron, but its more use- 
ful compounds. 



230 THE IRON GROUP. 

Let the chromite be heated with a mixture of potassium 
carbonate and potassium nitrate, and the potassium will 
take the place of the iron. In this way the ore, iron chro- 
mite, is changed into potassium chromate, K 2 Cr0 4 . This 
new chromate can then be washed out with water. The 
solution is very yellow, and when evaporated yields a 
highly-colored yellow salt. 

Now let a solution of this K 2 Cr 4 be treated with nitric 
acid. Its color will change from yellow to red (try it), and 
its substance will change from potassium chromate to 
potassium dichromate, K 2 Cr 2 7 . By evaporating the 
solution, fine orange-red crystals may be obtained. (Do 
this.) 

Compounds of Chromium. — The chromates generally 
are highly colored, and some of the insoluble ones are 
used as paints. The lead chromate, or " chrome-yellow " ? 
as it is known in commerce, is a good example. 

Ex. 168. — Make a solution of either potassium dichro- 
mate or chromate, in water, and add little by little some 
solution of lead acetate. The bright yellow precipitate is 
the pigment, chrome-yellow, PbCr0 4 . 

Salts, such as chromium sulphate, in which the chro- 
mium is basic, are sometimes violet-colored, sometimes 
green. 

Chrome alum is a quite common substance made of two 
sulphates, the chromium and potassium sulphates. It has 
a fine violet color. From this compound we can easily 
get chromium hydroxide, which is green. Thus : 

Ex. 16 4- — To a solution of a little chrome alum in 
Avater, add, little by little, some ammonium hydroxide. 
Notice the bluish-green precipitate of Cr 2 (HO) 6 . 

Is this, like the zinc hydroxide, soluble in excess ? 
Is it, like the manganese hydroxide, soluble in Am CI ? 



THE IRON GROUP. 231 

Will it, like the ferrous hydroxide, turn red when ex- 
posed to air ? 

Can you get the same precipitate by K H instead of 
KH 4 HO? 

And if so, is it soluble in excess of K H ? 

Ex. 165. — To a solution of a little chrome alum in 
water acid Am 2 S, little by little, and compare this pre- 
cipitate with that in the last experiment. It is the same 
substance. 

There is a chromium sulphide, Cr 2 S 3 , but it cannot be 
made in the presence of water, like the sulphides of man- 
ganese, zinc, and iron; the hydroxide will come instead. 

THE IRON GROUP. 

The five metals — iron, manganese, nickel, cobalt, and 
chromium — are closely related, and, together, form the 
Iron Group. 

The metals in this group are much alike in color, luster, 
and hardness, and much alike in chemical behavior. For 
example, they all unite with oxygen, and in more propor- 
tions than one, making oxides which are sometimes basic 
and sometimes acid. 

But their affinity for oxygen is not equally strong, for 
while chromium and manganese rust quickly when exposed 
to moist air, iron does so much more slowly, while nickel 
and cobalt will keep their luster unless heated. It is in- 
teresting to note that this order of the metals, in their 
behavior with oxygen, is also the order of their combin- 
ing weights. Thus : 



Cr 


Mn 


Fe 


Ni 


Co 


52 


55 


56 


58 


59 



Another fact is curious : these atomic weights are nearly 
alike. In other groups we have not found it so. Look, for 
example, at the potassium and the calcium groups. 



232 THE IRON GROUP. 

Suggestions. — If the student has made the experiment with 
the ammonium sulphide, Am 2 S, he has seen how very different 
are the sulphides of zinc, manganese, iron, and chromium. And 
if he has used ammonium hydroxide, NH 4 HO, he has also seen 
how very different are the hydroxides of these metals. Now, by 
the experiment with these two reagents, he ought to be able to 
tell with considerable certainty whether any substance which is 
given him is a compound of one or another of these metals. 

Let him try to do this by taking specimens from the teacher or 
a friend who knows what they are. Nickel and cobalt may also 
be included in the list, if thought best. 

If the substance given will not dissolve in water, perhaps you 
can change it into another compound, of the same metal, which 
will. Ferrous sulphide is not soluble in water, but hydrochloric 
acid will change it into ferrous chloride, which is. Now, sup- 
pose you do not know that the specimen is ferrous sulphide, and 
yet you wish to find out if it is a compound of iron or of some 
other metal. You can treat it with a little hydrochloric acid and 
get a solution of the chloride, and then you can use the Am 2 S 
and the N H 4 H O. 

If hydrochloric acid will not answer, you can use nitric acid, 
or even aqua regia, to get the substance into solution. But in 
all cases, just as little of these acids as possible should be used. 



AI^UMINUM. AT'. 

Aluminum is a beautiful blue metal, with a luster like 
silver. It can be hammered into thin sheets, or drawn 
into fine wire, or cast into any desired form, like iron. It 
is one of the light metals ; it is only 2.56 times heavier 
than water. It does not easily tarnish in air, and it melts 
only at a high temperature. 

At the same time that it has all these valuable proper- 
ties, aluminum is one of the most abundant metals. It 
is found combined with silica in clay, and in all slate 
rocks, which are little more than hardened clay. In fact, 
about one-twelfth the weight of the solid parts of the" 
earth is aluminum. 

But there is no cheap way to get this metal from its 
ores, and it is, therefore, too costly to be used in the arts, 
in place of silver and iron, for many purposes, as it would 
otherwise be. Its use is limited to ornamental work, and 
to small articles of apparatus where strength with light- 
ness are required. 

Compounds of Aluminum — Alum is the most useful 
compound of this metal. Alum is really a compound of 
two sulphates and water, for it is potassium and alumi- 
num sulphate with much "water of crystallization." Its 
formula is K 2 Al 2 (S 4 ) 4 + 24 H 2 0. This is the common 
alum, although " ammonium alum" is also much used in- 
stead; it has ammonium in place of potassium. 

Aluminum oxide, or alumina as it is usually called, is 
found in the rocks in beautiful crystals, having different 
colors and known by different names. The topaz and the 
emerald are examples ; the first is yellow and the second 
green, but both are alumina. So are the oriental amethyst, 

233 



234 ALUMINUM. 

which is purple, the sapphire, which is blue, and the ruby, 
which is red. 

Some compounds of aluminum are largely used in oper- 
ations of calico printing and dyeing. This is true of the 
sulphate and the hydroxide. 

The following experiments will reveal some of the chemi- 
cal characters of the aluminum compounds. 

Ex. 166. — Make a dilute solution of alum, and add, little 
by little, ]ST H 4 H 0. The white gelatine-like precipitate is 
aluminum hydroxide, Al 2 (H 0) 6 . 

Is this Al 2 (HO) 6 soluble in excess? 

Can you get it by means of KHO instead of NH 4 HO? 

And if so, is it soluble in excess of KHO? 

Ex. 167. — Make a dilute solution of alum as before, and 
color it just distinctly red with a solution of cochineal. 
Then add 1ST H 4 H 0. The aluminum hydroxide now com- 
bines with the coloring-matter of the cochineal. It is red, 
while the liquid is left colorless. 

The color cannot be washed out of the hydroxide. Now, 
it is this fact which makes the aluminum salt useful in 
dyeing. For if cloth is first soaked in a solution of alum 
and coloring-matter, and then plunged into a solution of 
ammonia, the same reaction will take place in the fibers 
of the fabric, from which the color cannot afterward be 
washed out by water. 

Ex. 168. — To a dilute solution of alum add a few drops 
of Am 2 S, and compare the precipitate with that in Ex. 167. 
It is the same substance. 

There is a sulphide of aluminum, A1 2 S 3 , but water 
decomposes it at once, changing it to the hydroxide. On 
this account the sulphide cannot be made in solutions. In 
this respect aluminum is like chromium. 



THE ANTIMOI^Y GROUP. 

Antimony. Sb'". — This metal is now and then found 
native, but it is oftener found in combination with sulphur 
or oxygen. The chief ore is the antimony sulphide, Sb 2 S 3 . 

The metal has a silvery appearance, quite brilliant, 
but, unlike silver, it is very brittle. Its alloys are more 
important than itself. We only need to mention type- 
metal, which is far the most important of all alloys, since 
the art of printing depends upon it. Antimony, tin, and 
lead are melted together to make this alloy, from which 
all types for printing are cast. 

There are three oxides of antimony, and these are all 
inclined to form acids rather than bases. This shows that 
antimony is more like the non-metals than any other metal 
which has yet been described. Another evidence of this is 
the fact that antimony combines with hydrogen, just as do 
nitrogen and phosphorus. The compound is called stibine, 
and its formula is H 3 Sb. Stibine may be made and burned 
just like arsin^ Ex. 123, and it then yields a stain of anti- 
mony on porcelain by Marsh's test, p. 181. 

Bismuth. Bi"'. — This metal is crystalline, brittle, and 
bright, with a reddish color. Bismuth, like antimony, forms 
an alloy with lead and tin. This alloy is called fusible 
metal, and it merits this title because it melts at a tem- 
perature of only 94° C. The separate metals must be 
heated much higher: tin melts at 228°, bismuth at 267°, 
and lead at 325°, but this alloy at 94°. Such is very 
generally the case with alloys : they melt more easily 
than any one of the metals of which they are made. 

235 



236 THE ANTIMONY GROUP. 

Fusible metal, like type-metal, expands when it becomes 
solid, and on this account it is used for taking casts 
from medals. When cast in a mold it expands into every 
line, and makes a most beautiful and faithful copy. 

Bismuth, like a true metal, forms bases, and, like a non- 
metal also, it forms acids. But its metallic nature is much 
more distinct than that of antimony, since it is less likely 
to form acids. This is also shown by the fact that it has 
no compound with hydrogen. 

The Group Bismuth and antimony are much alike, 

and, 'as we have just seen, both have the properties of 
non-metals. In fact, they agree closely with the nitrogen 
group. In bismuth the metallic properties are very clear, 
in antimony not so clear, in arsenic quite obscure, in phos- 
phorus and nitrogen altogether wanting. From bismuth to 
nitrogen, the transition from metal to non-metal is gradual 
and perfect. 

No better proof is needed that it is the chemist, and 
not nature, who divides the elements into these two great 
classes. 

Such a division, however, is convenient. But chemists 
do not all agree as to just w r here the line shall be drawn. 
Some have put arsenic among the metals ; others have put 
arsenic, and antimony too, among the non-metals. 

In this book the line has been drawn between arsenic 
and antimony. Because, then, we have on one side, all the 
elements whose compounds with oxygen and hydrogen are 
acids, and on the other, all those whose compounds with 
oxygen and hydrogen are ever bases. The oxides of arsenic 
are always acid, while one of the oxides of antimony is 
basic, — feebly so to be sure, but truly basic. 

Compare their Eeactions. — Some of the chemical 
actions of bismuth, antimony, and arsenic will be a useful 
study by experiment. 



THE ANTIMONY GROUP. 237 

Ex. 169. — Arrange three tubes each with about 10 cc. 
of water. Into one put a few grains of arsenous oxide ; 
shake it well, and if it does not dissolve, heat it. It 
dissolves to a clear solution. 

Into a second tube put a few grains of bismuth nitrate ; 
shake it well: you find the liquid changed to a milky 
whiteness, instead of a clear solution. To this then add 
strong hydrochloric acid, drop by drop, and it will soon 
become perfectly clear. 

Into the third tube put a few drops of antimony chlo- 
ride ; this liquid also at once becomes white. But add 
hydrochloric acid as before, and it becomes clear. 

The compounds of bismuth and antimony are decom- 
posed by water, but of arsenic not. This effect of water is 
not common. The white solids, precipitated by water, are 
soluble in hydrochloric acid. 

These three clear solutions may be used in the follow- 
ing experiments. We will first study the sulphides, as 
follows : 

Ex. 170. — Fit up the apparatus for hydrogen sulphide, 
Ex. 107. Put an arsenic solution — enough to cover the 
end of the glass tube — into flask a, and add a few drops 
of H CI. Put an antimony solution, made clear by H CI, 
into flask b, and a bismuth solution, also made clear by 
H CI, into flask c, and then pass the H 2 S gas through 
them all. 

Observe that the sulphides of all three metals are 
produced, and notice their different colors. 

These are the first sulphides which we have found to be 
insoluble in acid water. And of these, one, the orange-red 
antimony sulphide, is soluble if much H CI is present. 

Ex. 171. — Let the sulphides settle, and then pour off 
the liquid; add considerable water to each. Let the 



238 THE ANTIMONY GROUP. 

sulphides settle, and decant the liquid again. We repeat 
this work in order to wash the sulphides clean : do it once 
more. Now pour yellow ammonium sulphide, (XH 4 ) 2 S, 
upon each, and gently warm it. The question is, whether 
the sulphides are soluble in this liquid. The bismuth 
sulphide will remain unchanged, but the other two should 
disappear ; they are soluble in yellow ammonium sulphide. 

Ex. 172. — Next compare the hydroxides. For this pur- 
pose make three clear solutions, as in Ex. 169, only be 
more careful to not use more H CI than just enough to 
dissolve the white precipitates. Then add N H 4 H 0, little 
by little, to each. Observe the difference between the 
arsenic and the other two solutions. 

Queries. — By what experiments could you decide whether a 
given substance is a compound of aluminum or of chromium? 

By what experiments could you decide whether a given sub- 
stance is a compound of aluminum or of iron? 

If a given substance is a compound of aluminum, or else of a 
metal in the antimony group, by what experiment could you 
decide which it is? 

Suggestions. — Take one or more specimens from the teacher 
or a friend who knows what they are, and decide, by experiments, 
whether each is, or is not, a compound of aluminum. 

Take specimens, which may be compounds of any one of the 
metals in the antimony group, and, by experiments, decide which. 



TIX ANT> LEAD. 

Tin. Sn" Tin seems to have been known since the 

earliest periods of history. 

It was called Jupiter by the old alchemists, and stem 1 by 
the people of Phoenicia. The people, just named, dis- 
covered tin in Britain more than a thousand years before 
the Christain era. 

Tin is found in the form of tinstone. Tinstone is a 
compound of tin and oxygen, Sn 2 ; it is the chief ore 
of the metal. 

The ore of tin is found in Cornwall, England, which 
has been noted for its tin-mines for many hundred years. 
Bohemia, Saxony, and Malacca and Banca, in India, also 
yield the ore of this metal. In this country it seems to 
be very rare, but it has been found in New Hampshire and 
California. 

Extraction of the Metal. — To obtain tin from this 
ore WT>uld be a simple thing if the ore were pure ; for it 
is an oxide which can be reduced by carbon. But the ore 
is mixed with other matters, which make the process more 
difficult. 

To get rid of the rocky and earthy parts, the ore is 
stamped to powder under wooden stampers shod with iron, 
and then washed with water. To get rid of sulphur and 
arsenic, the ore is roasted and washed, perhaps twice. And 
then, to take away the oxygen, the roasted ore is melted 
with charcoal and lime. 

Properties of the Metal. — Tin is a silver-white 
metal with a fine luster, and somewhat harder than lead. 
It can be hammered into sheets so thin that a thousand 

1 The symbol for tin, Sn, comes from its old name Stan, or Stannum. 

239 



240 TIN AND LEAD. 

or more would be needed to make an inch in thickness. 
It does not tarnish readily in air, showing that its attrac- 
tion for oxygen is slight, but when heated, tin and oxygen 
combine at once. 

Because tin is so malleable it is much used in thin 
sheets, called tin-foil. But the tin-foil of commerce usually 
contains some lead, and sometimes a large proportion of 
that metal. 

Because air does not readily tarnish it, tin is used for 
coating iron to keep it from rusting. The "tin" of which 
common tin-ware is made is sheet-iron with a thin coat- 
ing of tin. 

Compounds of Tin. — There are two compounds of 
oxygen and tin ; one is called stannous oxide, Six" 0, the 
other is the stannic oxide, Sn //// 2 . There are also two 
chlorides, two sulphates, — in fact, there are two classes 
of tin compounds, the ous and the ic forms. 

Starting with the metal itself we can make several of 
the tin compounds and study by experiment their chemi- 
cal behavior. We will first study the chlorides. 

Ex. 173. — Place 5 cc. strong hydrochloric acid in a test- 
tube and drop into it a piece of granulated tin. Then heat 
until the effervescence is brisk ; after which keep the tube 
warm by holding it above the flame of the lamp until, 
when taken away from the heat, the bubbling nearly or 
quite stops. If, before this occurs, the tin is used up, 
another piece must be added. When the effervescence is 
brisk, a match-flame, brought to the mouth of the tube, will 
cause a slight explosion. 

What gas is set free by the action? 

Into what compound is the tin changed? 

Sn" + 2HC1 = Sn"Cl 2 + 2H. 
The SnCl 2 is stannous chloride. 



TIN AND LEAD. 241 

It is easy to change this ous chloride into the ic form 
just as ferrous was changed into ferric chloride, Ex. 157. 

Ex. 174- — Pour about 2 cc. of the SnCl 2 solution into 
another tube, add four or five drops of strong nitric acid, 
and boil the mixture a minute. 

Is there any evidence of a chemical change ? 

But we may go further and prove that stannous chloride 
is no longer present, in this way: 

Ex. 175. — Prepare two clean tubes with 10 cc. of water 
in each, and add to one about a cubic centimeter of the 
solution of stannous chloride of Ex. 173, and to the other 
about as much of the solution just now made. Next add, 
drop by drop, a solution of mercuric chloride to the first. 

What is the color of the precipitate by the first drop ? 

What change occurs when more and more are added? 

These are the changes which this reagent always makes 
in stannous chloride. Now add, to the other solution, 
some drops of mercuric chloride in the same way. No such 
changes should take place. Then it is plain that stannous 
chloride is not present. 

The fact is that the stannous chloride took the chlorine 
from the mercuric chloride, and so became stannic chloride. 
The white precipitate at first, was mercurous chloride, and 
the gray at last, was mercury itself. Thus : 



1. 


2HgCl 2 


-f SnCl 2 = 


= SnCl 4 


+ 


Hg 2 Cl 2 




Mercuric 


Stannous 


Stannic 




Mercurous 




chloride 


chloride 


chloride 




chloride 


2. 


Hg 2 Cl 2 


+ SnCl 2 : 


= SnCl 4 


+ 


Hg 



In this way mercuric chloride will always tell one 
whether a given solution of a compound of tin is stan- 
nous or stannic chloride. 

We will next study the sulphides. The two sulphides 
may be made by hydrogen sulphide. Thus ; 



242 TIN AND LEAD. 

Ex. 176. — To 10 cc. of water add £ cc. of the stannous 
chloride of Ex. 173. And again, to 10 cc. of water add 
\ cc. of the stannic chloride of Ex. 174. Then pass hydro- 
gen sulphide through both. 

The first gives stannous sulphide, Sn S, brown. 

The second gives stanic sulphide, SnS 2 , lemon yellow. 

It is plain that tin must be added to the list of metals 
whose sulphides are insoluble in acid water. 

Now try these sulphides with yellow Am 2 S. Are they 
soluble in it ? 

Eefer back to antimony, arsenic, and bismuth, to see 
which of these have sulphides, which behave in the same 
way, with Am 2 S. 

LEAD. rh". 

The lead ores of Spain and of England were worked by 
the ancient Romans, and still farther back, even before the 
sacred books of Exodus and Job were written, this metal 
was known and used. 

The ores of lead are many ; but for the most part they 
are not abundant. One of them, however, is found in 
immense beds and veins in the rocks. This ore is called 
galena. It is a compound of lead and sulphur, Pb S. 1 

Illinois, Iowa, and Missouri, to say nothing of several 
other of our States, have an abundance of galena stored 
away in their rocks. 

Extraction of Lead from its Ores To obtain the 

metal, the ore is roasted, on the floor of a furnace, with 
plenty of air. The hot oxygen changes a part of the sul- 
phide into sulphate and another part into oxide, while a 
third part remains as it was, — sulphide. 

The furnace is then shut tight, and the fire driven to a 

1 The symbol for lead, Pb, is from the Latin name of the metal, 
Plumbum. Lead is bivalent, Pb". 



TIN AND LEAD. 243 

greater heat. The new compounds, just mentioned, then 
attack and decompose each other, and all three of them 
give up their metallic lead. The way in which these 
three compounds reduce each other may be seen by writ- 
ing the reactions. The three substances made by roasting 
are PbS0 4 , Pb 0, and Pb S. 

Then PbS0 4 with Pb S become 2 Pb and 2S0 2 
and 2 Pb O " Pb S " 3 Pb " S 2 

The sulphurous oxide is carried away by the draught, 
while the melted lead remains covered with the earthy 
impurities of the ore, — a melted slag, from under which it 
may be drawn off. 

By Iron. — There is another way of getting the lead 
from galena, based on quite another principle. In fact it 
may be given to illustrate another method of metallurgy, 
p. 194. In this method one metal is used to liberate 
another. This is called the 'precipitation process. 

Some lead may be easily obtained by "precipitation," 
and the experiment will illustrate the fact that one metal 
may displace another from its compounds. Thus: 

Ex. 177. — Dissolve 8 g. or 10 g. of lead acetate, com 
monly called " sugar of lead," in about 500 cc, a pint of 
water, and if the solution is cloudy add a little 
acetic acid to clear it. Put this into a white 
glass bottle, and then hang in it a strip of 
clean sheet zinc (Fig. 66), and let it stand 
undisturbed. It will not be long before bril- 
liant crystals of lead may be seen on the sur- 
face of the zinc, but it should be left until 
to-morrow, that we may witness the beautiful Flg " 66 ' 
growth of crystals, which has long been called the lead-tree. 

Lead acetate and zinc, become zinc acetate and lead. 
This shows the precipitation of a metal " in the wet way." 




244 TIN AND LEAD. 

But in the case of lead ores, iron, instead of zinc, is 
used to liberate the lead, and the change is brought about 
by heat instead of in solution. The ore and scraps of iron 
are heated together in a blast-furnace, when the iron takes 
the sulphur away from the lead, thus : 

Pb S + Fe = Fe S + Pb 

This is the "precipitation" of a metal "by heat." 

Properties of Lead Lead is so soft as to be easily 

cut with a knife. Its freshly-cut surface shows that the 
metal has a light-blue color and a fine luster, which may be 
seen, in the crystals, in Ex. 177. It is a heavy metal, being 
11.4 times heavier than the same bulk of water. 

Its attraction for moist oxygen is quite strong, even at 
common temperatures, so that its surface is never bright 
except when freshly cleaned. But why say " moist " oxy- 
gen ? Because it is found that in perfectly dry air lead 
does not tarnish, and also that in water which contains 
no air it stays bright, which shows that both air and 
moisture are required. 

Lead Oxides. — Lead combines with oxygen to make 
three oxides. When heated in air the metal is changed to 
lead oxide, PbO, — a yellow powder known as litharge, 
which is used in making flint-glass, p. 185. 

There is also the lead dioxide, Pb0 2 , which is a brown 
powder, and then another oxide, Pb 3 4 , called minium, or 
red lead, which is used as a paint. 

Many of the lead-salts are insoluble ; in fact, the nitrate 
and the acetate are the only two, at all common, which 
will dissolve in water. From these two, the student can 
make other compounds of lead, and by so doing become 
acquainted with the chemical actions of this metal. 

Ex. 178. — To make the carbonate. First make a dilute 
solution of lead acetate, and make it clear by acetic, acid 



TIN AND LEAD. 245 

if need be, but use just as little acid as will answer this 
purpose. Then add some ammonium carbonate. The 
white solid obtained is "lead carbonate." 

But it is found that this lead carbonate is not a pure 
carbonate ; it contains lead hydroxide also. It is often 
called the basic carbonate. This basic carbonate is the 
" white lead " which is so much used as a paint. 

Salts which contain an hydroxide are called basic salts. 

Ex. 179. — To a dilute solution of lead nitrate l add 
ammonium hydroxide. The white precipitate is not a 
pure hydroxide : it contains lead nitrate also. It is an- 
other basic salt, called the basic nitrate. 

Of what other metals are the hydroxides white ? 

Is this lead precipitate soluble or insoluble in excess ? 

What other hydroxides are like it in this respect ? 

Ex. 180. — To a dilute solution of lead acetate add drops 
of hydrochloric acid. No precipitate should appear. But 
now use hydrogen sulphide. The black precipitate which 
falls is lead sulphide, PbS. 

What other metals have given sulphides by H 2 S in acid ? 

Which of these other sulphides does this lead sulphide 
resemble in color ? 

Will Am 2 S dissolve this lead sulphide ? 

Ex. 181. — To a strong solution of lead acetate add drops 
of hydrochloric acid. A white precipitate appears : it is 
lead chloride, Pb Cl 2 . Now heat the mixture, and observe 
that the chloride disappears. Let it cool again, and see 
that the chloride returns in the form of needle-shaped 
crystals. Why did not drops of H CI make a precipitate 
of this chloride in Ex. 180, as well as in this one ? 

All this proves that lead chloride is somewhat soluble 

1 Make the lead nitrate by adding drops of HN0 3 to the basic 
carbonate of Ex. 178, until the white substance is dissolved. 



246 TIN AND LEAD. 

in cold water (Ex. 180), but not freely (Ex. 181), while in 
hot water it dissolves largely (Ex. 181). 

Have we found any other metal, so far, whose chloride is 
insoluble ? 

If a solution contains either Bi or Pb, can you tell which 
by Ex. 181? 

If a solution contains Bi or Pb, can you tell which by 
Ex. 180? 

Ex. 182. — To a moderately strong solution of lead 
nitrate add drops of potassium iodide. The bright yellow 
precipitate is lead iodide, which is very sparingly soluble 
in the cold. 

But heat the mixture and the iodide disappears. If 
there is water enough it will become perfectly clear. Now 
let the tube and contents cool, and watch it. 

Describe the iodide as it now appears. 

Why does the iodide reappear ? 

Lead is the only metal whose compounds yield, in this 
way, such a brilliant and crystalline iodide. Hence this 
experiment is an excellent test for lead. The appearance 
of rich yellow lead chromate, by the use of potassium 
chromate (Ex. 163), is another excellent test for lead. 

Query. — By what experiments could you decide whether a 
given compound is, or is not, a compound of tin or lead? 
Try it. 



THE COPPER GROUP. 

COPPER. Cu". 

Copper is often found in nature in the metallic state. 
This is the case in the noted copper-mines of Cornwall and 
Devon, in England. Some of the finest native copper in 
the world is found in the region of Lake Superior, where 
it occurs in great abundance. One single mass, of Lake 
Superior native copper, weighed over 400 tons. 

Native copper is crystalline. The separate crystals are 
usually little cubes, but in some cases the 
cubes are grown together in vast numbers 
making up quite large masses, and these 
masses often show most singular branch- 
like forms, sometimes rudely resembling 
the form of some growing plant. Eig. 67 
is the picture of a specimen. 

But copper, as native metal, is much less 
abundant in nature than are its ores. 

Copper pyrites, made of copper, 1 iron and 
sulphur, CuFeS 2 , is the ore which is most 
common. It is crystallized in cubes of per- 

J r Fig. 67. 

feet form, having the color and luster of 

brass. Besides this there are other sulphides, such as 

Cu 2 S and Cu S, also found in considerable quantity. 

Malachite is a rich ore of copper, less common than 
pyrites. It is a green stone, which takes a fine polish, and 
is often used for ornamental purposes. In composition it 

1 The symbol for copper is Cu, from the Latin name of the metal, 
Cuprum. 

247 




248 THE COPPER GROUP. 

is a basic carbonate, for it contains both the carbonate and 
the hydroxide of copper, CuC 3 , Cu (H 0) 2 . 

Other ores of copper are widely distributed. Some are 
blue, some are red, some are purple, some are gray, but we 
need not stop to describe them. 

Extraction of Copper. — The metal is extracted from 
its sulphide by roasting and reducing it in air. The ore 
is first roasted and then melted, and then roasted again ; 
this changes a part of the sulphide into copper oxide, Cu 0. 
This roasted ore is then mixed with sand and heated in 
a reverberatory furnace. The copper goes back into the 
form of sulphide while the iron of the ore takes oxygen, 
and, with the sand, becomes a liquid silicate. At the end 
of this repeated roasting the copper is still combined with 
sulphur, but it is rid of the iron. 

The rest of the operation is like that of getting lead. 
The sulphide is again roasted ; a part of it is changed to 
oxide, while the rest remains as sulphide, and then, by 
heating them strongly, these two compounds attack each 
other, and the copper of both is set free. Thus : 

Cu 2 S + 2CuO = 4Cu-f-S0 2 

Properties. — This metal has a peculiar deep red color, 
not to be seen in any other. It is rather soft, easily bent, 
very ductile, and very strong. It is one of the very best 
conductors, and this makes copper, more than any other 
metal, useful in all the applications of electricity. 

Alloys. — The alloys of copper are many and important. 
Brass is an alloy of copper and zinc ; German silver, of cop- 
per, zinc, and nickel ; while bronze, and bell-metal, and gun- 
metal, are made of different proportions of copper and tin. 

Copper Compounds. — Copper, when long exposed to 
moist air, turns green ; the green coating is a carbonate. 
The metal does not unite with oxygen at common temper- 
atures of the air, but when heated it does, and if intensely 



THE COPPER GROUP. 249 

heated, it slowly burns, giving a fine green color to the flame 
which heats it. This may be easily shown by holding a 
small copper wire for some time in the edge of the Bunsen 
flame. There are two oxides of copper : one is the cuprous 
oxide, Cu 2 0, which is red ; the other is the cupric oxide, 
Cu 0, which is black. So there are also two chlorides, two 
iodides, two sulphides, and, in fact, two classes of copper 
compounds, the cupr^s and the cupr/c. 

Cupric Sulphate. — The cupric sulphate is the most 
common salt of this metal. It is usually called copper 
sulphate. It comes in the form of blue crystals, Cu S O i + 
5 H 2 0. The blue color depends upon the water of crystal- 
lization, for when the water, 5 H 2 0, is driven off by heat, 
as it may be very easily, the substance is white. This 
salt goes under the common name of "blue vitriol/' just 
as the ferrous sulphate is called " green vitriol," and as the 
zinc sulphate is called "white vitriol." 

Study of Some Reactions of Copper. — Starting with 
the copper sulphate the student can produce several of the 
compounds of copper, and in this way become acquainted 
with some of the chemical peculiarities of this metal. 

Ex. 188. — Keduce a little copper sulphate to powder 
and dissolve it in water little by little. First see how little 
will be needed to give a perceptible blue color to, say 10 cc. 
of cold water in a tube. Then add more and more until 
it no longer disappears when shaken. 

Many other copper compounds in solution have the same 
color as this one. Indeed, when this blue color is seen in 
a liquid it is a sign of the presence of some copper com- 
pound, — not a proof, but a sign. This solution may be used 
for the experiments which follow. 

Ex. 18 Jf. — Add a cubic centimeter of the copper sulphate 
solution to 10 cc. of water. Into this put slowly, one, two, 



250 THE COPPER G1WUP. 

three drops of ammonium hydroxide, and shake it well. 
The precipitate, which is deep blue when just enough of 
the reagent is used, is copper hydroxide, Cu (H 0) 2 . With 
too little reagent the precipitate is pale blue. 

Is this hydroxide soluble in excess ? 
Compare this result with the effect of ammonia on 
zinc, nickel, and cobalt, hydroxides. 

Compare it also with lead and bismuth hydroxides. 

Ex. 185. — Add a cubic centimeter of the copper sulphate 
solution to 10 cc. of water, and a few drops of hydrochloric 
acid. 

Note the evidence that copper chloride is soluble. 
Then add hydrogen sulphide : black Cu S is made. 

What other metals have given sulphides in acid water ? 
Which of those others does this Cu S most resemble ? 
Find out whether it is soluble or insoluble in Am 2 S. 

The same brown-black sulphide is made when Am 2 S is 
added directly to the original solution of cupric sulphate : 

CuS0 4 +(NH 4 ) 2 S = CuS + (NH 4 ) 2 S0 4 

and ammonium sulphate (NH 4 ) 2 S0 4 is also made, which 
remains dissolved. 

Ex. 186. — Place a bright piece of iron wire, or a knife- 
blade, in a dilute solution of copper sulphate in water : 
it is soon coated with red metallic copper. Leave it in 
until the blue color is all gone from the liquid. Then try 
a fresh piece of bright iron. It will need some time, but 
the iron will take every particle of copper out, so that 
this fresh piece will not be coated at all. 

CuS0 4 + Fe = Cu + FeS0 4 

Now by this reaction we see that, besides the metallic 



THE COPPER GROUP. 251 

copper, Cu, some ferrous sulphate, FeS0 4 , must be made 
at the same time. 

Does the color of the liquid suggest the presence of an 
iron compound ? See Ex. 155. 

Can you prove, by experiment, that it does contain iron ? 

MERCURY. Hg". 

Mercury * is sometimes found in the earth as native 
metal, but oftener in combination with sulphur. The sul- 
phide, Hg S, is its chief ore, and it is called cinnabar. The 
color of this ore is* dark red, and in some specimens it is 
almost as rich and brilliant as vermilion. Indeed, these 
two things have the same composition; cinnabar is the 
native sulphide, vermilion is the artificial sulphide. The 
ore is found in many countries; Spain, Austria, China, 
and California are examples. 

Extraction of the Metal Mercury is easily obtained 

from cinnabar. The ore only needs to be roasted, when 
this reaction will occur: 

The ore is decomposed by the hot air ; its sulphur burns 
off as sulphurous oxide, while its mercury is left free. 
The metal is then in the form of vapor, which is led into 
cold vessels, where it becomes liquid. 

Properties. — Mercury is a liquid, — the only liquid 
metal. It is tin-white, with a splendid luster. It is very 
heavy, — thirteen and a half times heavier than the same 
volume of water. When cooled down to — 39.5° C. it freezes 
to a white lustrous solid; when heated to 350° C. it boils. 

With some other metals it makes alloys, but the alloys 
of mercury are generally called amalgams. Zinc, copper, 

1 The symbol for mercury, Hg, is taken from the Latin Hydrar- 
gyrum. 



252 THE COPPER GROUP. 

silver, and gold are changed into amalgams at once by 
contact with mercury. 

Compounds of Mercury Mercury does not tarnish 

in air unless heated, but if kept at almost boiling heat, 
it is changed into mercuric oxide, HgO, known as the 
"red oxide," Ex. 5. This metal also forms two series of 
compounds, the ic and the ous. Thus we find mercuric 
chloride and mercurous chloride, mercuric and mercurous 
sulphates. 

Mercuric chloride, Hg Cl 2 , is the virulent poison, known 
under the name of corrosive sublimate. 

Mercurous chloride, Hg 2 Cl 2 , is the medicine known 
under the name of calomel. 

Both of these are white solids, and when seen in powder 
are alike in appearance, but the poison is soluble in water, 
while the medicine is insoluble. 

Mercurous Compounds. — The metal mercury is soluble 
in nitric acid, which, if dilute, changes it to mercurous 
nitrate. 

Ex. 187. — Put a small globule of mercury into a tube, 
and add a cubic centimeter of dilute nitric acid. Then 
heat it. The mercury will slowly waste away, and, if need 
be, let more acid be added, but not too much, so that 
the metal shall be completely dissolved. 

This solution of mercurous nitrate may be used as 
follows : — 

Ex. 188. — Add a few drops of it to 5 cc. of water, and 
then add drops of hydrochloric acid. The white solid 
obtained is mercurous chloride, or calomel, Hg 2 Cl 2 . 

What other metal yields a precipitate with H CI? 

Is this chloride, like that one, soluble by boiling ? 

Now add to the white chloride a little ammonium 
hydroxide and note the marked change in color. This is 



THE COPPER GROUP. 253 

the only white chloride which will turn black when 
treated with ammonia. 

Ex. 189. — Add a few drops of the nitrate to 5 cc. water, 
and then add ammonium hydroxide. The same black 
precipitate is made at once. 

Mercurous compounds are the only ones which yield 
black precipitates with ammonia. 

Mercuric Compounds. — A solution of corrosive subli- 
mate, mercuric chloride, may be the starting-point in our 
study of the chemical actions of mercuric compounds. 

Ex. 190. — Add a cubic centimeter of mercuric chloride 
to 5cc. of water. Add also drops of hydrochloric acid. 
]S~o precipitate will appear. 

Can you explain the fact that H CI can make no precipi- 
tate in any mercuric compound ? 

Finally add hydrogen sulphide, and notice any changes 
of color which may occur. At first the precipitate may 
be white, but with more and more H 2 S it will become 
yellow, brown, and at last black. The mercuric sulphide, 
HgS, when well formed is black. 

What other metals have given black sulphides by H 2 S ? 

Ex. 191. — Add a cubic centimeter of Hg Cl 2 to 5 cc. of 
water, and then use NH 4 HO, little by little, to excess. 

What is the difference between the actions of N" H 4 H 
on the mercurous and the mercuric compounds? 

Ex. 192. — To another dilute solution of the HgCl 2 add 
one drop of hydrochloric acid, and then put into it a 
piece of bright copper wire. 

Notice the coating which soon gathers on the wire. 

What is it ? Its appearance, especially when rubbed, 
will be likely to inform you. So will the reaction if it 
be written, thus : 

HgCl 2 + Cu = CuCl 3 -f Hg. 



254 THE COPPER GROUP. 



SILVER. Ag*. 

Silver is sometimes found in the native sta,te. Such 
specimens are often very beautiful, looking like metallic 
twigs and branches. But this metal is more abundant in 
combination, sometimes with chlorine, but oftener with 
sulphur. The sulphide of silver is sometimes found alone, 
but, in most cases, it is in company with the sulphides of 
other metals, such as lead and copper. These mixed 
sulphides of silver and other metals are the chief ores of 
silver. 

Silver is almost always present in galena, and much 
silver is obtained from that ore. 

Extraction of the Metal There are different ways 

of taking silver from its ores. We will study two of 
these. 

First suppose the silver is to be taken from its sulphide, 
which contains the sulphides of other metals, as it usually 
does. Can the ore be treated the same as the ores of 
zinc or lead, — that is, changed to an oxide by roasting 
in air? No, because silver, unlike those metals, has very 
little attraction for oxygen. But it has a very strong 
attraction for chlorine, and this fact is made use of to 
get the metal away from the sulphur in its ore. 

For this purpose, the ore is well stamped, to crush it 
to powder, and then mixed with a little — about one 
tenth its weight, common salt — sodium chloride. The 
mixture is then heated, and, to make sure that the work 
is well done, the ore is mixed with more salt and heated 
again. In this operation, the chlorine of the salt seizes 
the silver of the ore, and holds it in the form of silver 
chloride. 

The next thing is to take the chlorine away, and iron 
is used for this purpose because chlorine has a stronger 



THE COPPER GROUP. 255 

attraction for iron than for silver. The chloride of silver 
is put into strong oaken casks, with a little water and 
fragments of iron. This mixture is violently shaken by 
turning the casks rapidly, and, under this treatment, the 
iron robs the silver of its chlorine. The silver is thus 
left free, but it is in very fine particles scattered through 
the mixture in the casks. How shall it be collected? 

Just at this point the use of mercury comes in. Mercury 
is poured into the casks, which are then set rotating again 
faster than before. This brings the silver and mercury 
together, and they at once combine to form an amalgam, 
p. 251, and the next thing is to get the silver out of this 
amalgam. 

To do this it is only necessary to heat the amalgam, 
when the mercury will pass off as vapor while the silver 
will be left behind. 

But the metal is still mixed with such other metals, — 
copper, iron, and antimony, as were in the ore. These must 
be removed, and so the metal is mixed with lead, and again 
melted while a current of air is driven over its surface. 
The oxygen seizes the lead and other metals, but not the 
silver, which is thus left pure. 

Silver from Galena. — But much of the silver now 
in use comes from the lead ore, galena. When the lead 
is obtained from this ore by the method described, p. 242, 
the silver comes with it, and then the problem is, how to 
get the small quantity of silver out of the large mass of 
lead. 

The lead is melted, and then allowed to slowly become 
cold. When it cools, crystals begin to form, and these 
crystals are pure lead. These crystals of lead are taken 
out with a strainer. They are melted over again, and 
again cooled ; another crop of pure lead crystals is then 
taken out, and this heating, and cooling, and dipping out 



256 THE COPPER GROUP. 

pure lead is continued, the silver every time remaining in 
the molten mass, until what is left behind is quite rich 
in the precious metal. 

And then oxygen is called upon to take away the lead 
that remains. The rich alloy is melted on a bed of bone- 
ash, and hot air is driven over it. The hot oxygen seizes 
the lead, but does not combine with the silver. The lead 
oxide soaks into the porous bone-ash and leaves the pure 
silver behind. This method of separating silver from lead 
is called cupellation. 

Properties of Silver. — Silver is the whitest of metals. 
It is ten and a half times as heavy as water/ It is much 
harder than gold, and very malleable and ductile. 

Oxygen does not attack it even when hot ; but its surface 
will quickly blacken in the presence of hydrogen sulphide 
because silver and sulphur strongly attract each other. 

Articles of silver-ware and silver coin are well known. 
But we must remember that none of these are made of pure 
silver. The pure metal is quite too soft to be able to stand 
the wear which these things receive. To harden the silver, 
small portions of other metals are mixed with it. 

For silver coin, some copper is added to harden the 
precious metal. In this country the standard coin metal is 
made of silver 90 parts and copper 10 parts. In England 
the proportion of copper is less (7.5), in Germany it is 
more (12.5). 

Compounds of Silver The most important com- 
pound of silver * is the nitrate, Ag N" 3 , and this is made 
by the action of nitric acid on the metal. This action 
begins instantly on putting the two together, and goes 
on vigorously until one or the other is exhausted. 



Ag + HN0 3 = 


= AgN0 3 


+ H 


H + HNO s : 


= H 2 


+ NO 



1 The symbol for silver is Ag, from the Latin name Argentum. 



THE COPPER GROUP. 257 

The silver takes the place of hydrogen in the acid, 
making the silver nitrate, Ag N" 3 , and setting the hydro- 
gen free, but this hydrogen instantly attacks another por- 
tion of nitric acid, and forms water and nitrogen dioxide. 
The liquid left is a solution of silver nitrate. By evapo- 
rating this liquid, transparent crystals of the silver nitrate 
may be obtained. 

Ex. 193. — To 10 cc. of water add 4 or 5 drops of silver 
nitrate, and then add drops of hydrochloric acid. A white 
precipitate forms at once : what is it ? 

Boil this precipitate, as lead chloride was boiled in Ex. 
181. Is it soluble in hot water, like lead chloride ? 

Add ammonium hydroxide to it, as was done with the 
mercuro^s chloride, Ex. 189. 

Does it blacken by ammonia, as the mercurous chloride 
did ? What is the effect of the ammonia on it ? 

By these differences, we can easily distinguish these 
three chlorides, one from another. 

Ex. 19 If. — To 10 cc. water add drops of silver nitrate, 
and then hydrochloric acid, or a solution of common salt, 
which will have the same effect. Place the tube with this 
white silver chloride in sunlight, and notice its change 
of color. 

Other silver salts are also very sensitive to the action 
of light. On this account the compounds of silver are 
much used in the art of photography. 

Separation of Silver and Copper. — We have seen 
that silver coin is an alloy of silver and copper. The two 
metals have been melted together : can we get them apart 
again, or prove that they are in the coin ? The student 
is now able to do this, and the work is an interesting and 
instructive exercise. 

Ex. 195. — Put a ten-cent piece in an evaporating-dish 
and cover it with a mixture of strong nitric acid and water, 



258 THE COPPER GROUP. 

half and half. Then heat gently, until chemical action 
begins. Describe the action, thus : 

What gas is set free ? What color does the liquid 
become ? 

What compound of silver is made ? What compound of 
copper ? 

When the chemical action is over, or nearly so, pour 
about 1 cc. of the blue liquid into about 5 cc. of water, and 
then add drops of hydrochloric acid, or, better, of solution 
of common salt, NaCl, until a drop no longer makes a 
precipitate. Let the precipitate settle, and then pour the 
liquid off into another tube. 

Wash the precipitate by pouring water upon it, shaking, 
and then, when it is settled again, pouring the water off 
into the waste. Do this a second time. 

Now you have the copper of the coin in the blue liquid, 
and the silver of the coin in the white precipitate. 

Prove that the blue liquid contains copper, by the use of 
iron, Ex. 186. 

Prove that the white precipitate is silver chloride by 
treating a part of it with hot water, another part with 
ammonia, and exposing another part to the sunlight. 

Suggestion. — Take specimens from the teacher or a friend 
who knows what they are, and, by experiment, decide whether 
each one is, or is not, a compound of lead, of silver, or of mer- 
cury. If it prove to be a compound of mercury, then decide 
whether it is a mercuric or mercurous compound. 



GOIiD AND PLATINUM. 

GOLD. A\i'". 

Gold is almost always found in the native state. Unlike 
the metals described before, this precious metal is very 
rarely found in combination with other elements : it is 
found as native metal. Yet this native gold is not pure ; 
it is mixed with silver, and sometimes, too, with copper, 
and often with other baser metals. Native gold is found 
in fine grains among the sands of certain rivers, and also 
in solid quartz rocks. jSTow and then a nugget of consid- 
erable size occurs. 

Extraction of Gold. — Gold is obtained from sands and 
other loose materials by the process called "washing." 
The material is put into a shallow pan and well stirred up 
with water. Gold is so heavy that the grains will quickly 
settle to the bottom, and then the earthy matter may be 
poured off from above it. Sometimes the gold-bearing 
deposit is washed by rocking it in a cradle through which 
a stream of water is slowly running. The lighter earth 
or sand is then washed away, while the heavy gold dust 
lags behind, and is caught in grooves in the bottom of 
the cradle. The precious metal is then dissolved in mer- 
cury, and afterward separated by heat. 

Gold is obtained from quartz rock by " amalgamation." 
The quartz rocks are crushed to the finest powder and 
then mixed with mercury. The mercury dissolves the 
gold and leaves the quartz. The amalgam of gold is then 
distilled, and the mercury goes away as vapor while the 
gold is left behind. 

Properties. — Gold is remarkable for its fine yellow 
color and beautiful luster. It is among the heaviest of 



260 GOLD AND PLATINUM. 

metals, about nineteen times (19.33) heavier than water. 
It is the most malleable of metals ; it is said that leaves 
have been beaten so thin that 280,000 would be needed 
to make an inch in thickness ! There is a curious fact 
about the color of gold-leaf ; it is this : looked at in the 
usual way it is yellow, but let a leaf be spread upon glass, 
so that it may be held up between the eye and a window, 
or the sky, and it will be. green. 

At a temperature of about 2000° F. (1102° C.) this pre- 
cious metal melts into a greenish-colored liquid. The 
highest heat of a furnace can scarcely change it into 
vapor, but the furious flame of the oxyhydrogen blowpipe 
can; its vapor has a purple hue. 

Few chemicals, even of the most corrosive character, 
can harm this noble metal. Oxygen cannot rust it; 
sulphur cannot tarnish it; nor can the strongest acids 
corrode it. For one element, however, it has a strong 
attraction; this is chlorine. On this account it dissolves 
readily in aqua regia ; in fact this liquid received its 
name, which means royal water, because it was found to 
dissolve gold, the "king of metals." It changes the 
gold to gold chloride, AuCV 1 

Gold is used for ornament and as money. But when 
pure it is almost as soft as lead, and hence unfit for 
either use. To make it harder a little copper or silver 
is added. The alloy used for coin in this country must 
be made of nine parts of gold to one part of copper. 

PLATINUM. Ft. 

Platinum is a still rarer metal than gold. In small 
quantities gold is very widely distributed in the earth, 
but platinum is found in few places. It is found in 
largest quantity on the slopes of the Ural mountains, and 

1 The symbol for gold is Au, from the Latin Aurum. 



GOLD AND PLATINUM. 261 

in Brazil and Peru. It is always found in the native state, 
but mixed with other metals, several of which, like osmium 
and iridium, are still rarer metals than itself. 

Pure platinum is silver-white. Oxygen cannot attack 
it at any temperature, and only the intense heat of the 
blowpipe can melt it. On these accounts platinum vessels 
are much used in the laboratory. Aqua regia and the 
caustic alkalies will dissolve platinum, and many other 
metals will form alloys with it, which melt more easily 
than the metal itself and are attacked by acids. 

The Platinum Group. — There are five very rare metals 
which are much like platinum in many of their properties. 
They are palladium, iridium, osmium, ruthenium, and 
rhodium. Palladium is remarkable for its action on hy- 
drogen. When heated to redness it absorbs this gas, and 
forms what seems to be a true alloy. And this fact would 
indicate that hydrogen is itself a metal. Accordingly it is 
sometimes called hydrogenium. 

Osmium is remarkable for its great weight ; it is the 
heaviest substance known, having a specific gravity of 
22.477. An alloy of osmium and iridium is found some- 
times in the sands with gold ; it is harder than steel, and 
is used for the tips of gold pens. 



CLASSIFICATION OF THE METALS. 

How Classes are made. — We have seen that some 
elements combine with oxygen and hydrogen to produce 
acids while others combine with oxygen and hydrogen to 
produce bases. If we put all those which produce acids 
together, and all those which produce bases together, we 
have all the elements in two large groups, — the non- 
metals and the metals. 

Now this illustrates the way in which classes are made. 
If the chemist has a large number of substances, he may 
find, by studying them separately, that several are alike 
in some important character; these he can put together 
to form a class or group. Others in the list will not agree 
with fchese, but while unlike them they will be like one 
another, and these he can put together to form a second 
class or group. And in this way he may at length have 
the entire list divided into groups, — each group holding 
only those individuals which are alike in the leading char- 
acter, however much they may differ in other particulars. 

The Classes of Non-Metals. — We have seen that 
the non-metals are placed in four groups, known as the 
chlorine group, the sulphur group, the nitrogen group, 
and the carbon group. The leading character, or, we may 
say, the foundation of this grouping, is valence. All uni- 
valent non-metals are put into one group, all bivalent 
non-metals into another, all trivalent non-metals into a 
third, and the quadrivalent non-metals into a fourth. 

The Metals not Classed in the Same Way. — Now 
the classification of the metals is also sometimes founded 
on valence. Then, all univalent metals go together into 
one group, all bivalent into another, and so on. But in 

262 



CLASSIFICATION. 263 

this book, the metals have not been grouped in this way, 
and the reason is, simply, that such groups of the metals 
would not best suit our particular purpose in the study of 
these elements. What we have wanted to do is to become 
acquainted with the general properties and behavior of the 
metals, and if they are grouped by their valence, metals 
quite different in properties and actions will sometimes 
be thrown together. As, for instance, silver is univalent, 
so are potassium and sodium, and all these will be in the 
univalent group if our classes are made by valence. 
But silver has few properties like the others. If we are 
studying the properties of the metals, it is better to put 
those together which are most nearly alike, and then silver 
will go with copper and mercury, instead of with potassium 
and sodium. 

More than One Way to Group them. — In fact, the 
classes of metals in this book are founded on likeness of 
properties, and not on valence. Thus we have the potas- 
sium group, because there are several metals which are 
all very much like potassium, — soft, light, alkaline ; and 
the calcium group, because there are several metals like 
calcium ; and the iron group, because the properties of 
iron are much the same as those of the other members. 
This is the most helpful way of grouping the metals 
when our object is to study their properties. 

But there must be some reason ivhy some elements are 
so much alike and others so different. There must be 
some reason why some are univalent, others bivalent, and 
others with still different degrees of valence. If we could 
only get at this cause of their differences, the elements 
would fall into natural groups. We could then know the 
place of every one of them in the true system of nature. 
But the chemist does not yet know this cause. He knows 
the facts only. On this account the true system of the 



264 CLASSIFICA TION. 

elements in nature is still beyond his reach. And until 
he reaches it, the elements will be classified in different 
ways, as different leading facts are chosen on which the 
classes may be founded. 

Four Ways to Classify the Metals. — There are, in 
fact, four important ways of classifying the metals. One 
way is founded on valence; a second way is founded on 
likeness of properties ; a third way is founded on atomic 
weights ; a fourth way is founded on the solubility of com- 
pounds. 

We need not stop longer with the first two of these; 
the third and fourth are yet to be described. The third 
is important because it includes all elements, metals and 
non-metals alike, in one system, and comes nearer than 
any other to being the "natural" system. The fourth 
is important because it is used in chemical analysis. 

THE NATURAL SYSTEM. 

Classification by Atomic Weights We have seen 

that the elements chlorine, bromine, iodine, and fluorine 
are very much alike in properties. They also combine with 
the same elements and in the same proportions. But while 
they have many of the same properties they have them in 
different degrees. Fluorine is the most active, chlorine 
next, then bromine, and finally iodine is least active of 
all. Their properties vary in this order. And we have 
also noticed the fact that their atomic iveights vary in the 
same order. The same fact has been noticed in our study 
of other groups. 

Newland's Discovery. — Such facts led Mr. Newland 
in 1863 to arrange many of the elements in the order of 
their atomic weights, beginning with the one whose atomic 
weight is least, and then, on looking over the list, he dis- 
covered that the elements with like properties were scat- 
tered at about equal distances apart. 



CLASSIFICATION. 265 

Let us leave out hydrogen and begin with lithium, whose 
atomic weight is next larger than that of hydrogen, and 
put 'the atomic weights under the symbols of the elements 
in the order of value, and we have 



Li 


Be 


B 


C 


N 





F 


Na 


7 


9 


11 


12 


14 


16 


19 


23 



But sodium, Na, is like lithium, Li. Both are metals of 
the alkalies, and univalent. Now begin with sodium and 
go on: 

Na Mg Al Si P S CI K 

23 24 27 28 31 32 35.5 39 

But potassium, K, is like sodium and lithium, alkaline 
and univalent. These properties are found in every 
seventh metal in the list so far, and not in any between. 

Let us write the list, of the first twenty-one, in lines 
of seven. Thus : 

Li = 7 Be = 9 B = 11 C = 12 N= 14 O = 16 F =19 
Na = 23 Mg = 24 Al = 27 Si = 28 P = 31 S =32 CI =35.5 
K =39 Ca=40 Sc=44 Ti=48 V = 51 Cr = 52 Mn = 55 

And we find that the elements which are most alike fall 
together, under one another, as lithium, sodium, and potas- 
sium in the first column, and fluorine and chlorine in the 
last. 

It is a curious fact that if we add 16 to the atomic 
weight of lithium, we get that of sodium, with the same 
properties. Add 16 again, and we get the atomic weight 
of potassium, another element with the same properties. 
Add about 16 to the atomic weight of any one and we get 
the atomic weight of another which has similar proper- 
ties. This is true until we reach phosphorus, when we 
must begin to add 20 instead of 16. 



266 CLASSIFICA TION. 

Mendelejeff's Table. — Now the Eussian chemist, 
Mendelejeff, went so far as to make a table of all the 
known elements in the order of their atomic weights, 
and he found that all those elements, which are most 
alike, then fell into the same column. The horizontal 
lines of elements in this table are called "series" and 
the columns are called "groups" In all there are 12 
series and 8 groups. Three of these series are given on 
p. 265, and in them are the first three members of seven 
groups. The fact is that — 

If all the elements are placed in the order of their atomic 
weights those which are most alike will be found at regular 
distances apart. As the atomic weights increase, the same 
properties appear, again and again, at regular intervals. 
This is known as the periodic law. 

The Spiral of Elements. — The table of elements has 
been made in many shapes. The spiral form, 1 Fig. 68, 
shows the main point very clearly, which is, that the 
elements fall naturally into groups as their atomic weights 
vary by regular additions. 

We begin with lithium at the center, and wind our way 
around the spiral, to the left, until we come out at the 
circumference. Along the way we pass by elements with 
larger and larger atomic weights in regular order. The 
spiral is divided into eight sections by lines from the 
center, and the elements which are alike in properties 
are found together in these sections. In fact, this con- 
tinuous spiral of atomic weights throws all the elements 
into eight natural groups. 

Take, for example, our chlorine group, p. 147, whose mem- 
bers have been found to be so much alike. We find them 

1 First given by Baumhauer in 1870, then modified by Huth in 
1884, and adopted by Carnelly in 1885, — Chemical News, Vol. 53, 
p. 184. 



CLASSIFICATION. 



267 



all in the seventh group of the spiral, brought there by the 
order of their atomic weights. We find all the members of 
the oxygen group in the sixth, all of the nitrogen group 
in the fifth, and all of the calcium group in the second. 




Fig. 68. 



But in each of these " natural groups " in the spiral 
we find some elements which have not before been put 
together. In the first, for example, we find all the metals 
of the potassium class, and with them, copper and silver. 
Now many of the leading properties of copper and silver 
are not like those of sodium and potassium. They do not 



268 CLASSIFICATION. 

agree with these in being soft, light, and combustible on 
water. Yet in some things they do agree quite closely. 
For example : 

Potassium forms the oxide K 2 
Copper " « Cu 2 

Silver " " Ag 2 

In these compounds the atoms of potassium, copper, and 
silver hold the same relation to oxygen. And the order 
of their atomic weights brings them together in the same 
group in the spiral. 

The Vacant Places. — There are many vacant places 
in the spiral : what is the meaning of these gaps ? They 
lead us to think that the elements are not yet all 
discovered. 

When the table was first made there was a vacant place 
where gallium, Ga, now stands in the third group. Men- 
dele jeff said that there ought to be an element whose 
" atomic weight is about 69, its specific gravity about 6, 
and its atomic volume about 11.5," to fill this gap. After- 
ivard gallium was discovered. Its atomic weight proved to 
be 69.8, its specific gravity 5.9, and its atomic volume 11.8. 
From its vacant place in the table, Mendelejeff was able 
to give the properties of this metal before it had been 
discovered. He did the same thing for the element scan- 
dium, Sc, also in the third group. Possibly other elements 
are yet to be discovered by which other gaps will be 
filled. 

THE ANALYTICAL SYSTEM. 

Classification Founded on Solubility. — We have 
found that hydrochloric acid will give a precipitate if 
mixed with a solution of a compound of silver, Ex. 193, 
but none if mixed with a solution of a compound of copper, 
Ex. 185. This is because silver chloride is insoluble in 
the liquid used, while copper chloride is soluble. 



CLASSIFICATION. 



269 



Now all metals whose chlorides are insoluble, like that 
of silver, can be put with silver to form one group. Such 
differences in solubility throw the metals together into 
classes called the analytical groups. 

But we have found, by experiment, what many of the 
insoluble compounds of the metals are, and Ave can see, 
from our experiments, which are alike and which not 
alike. Indeed, if we will just gather up the facts which are 
scattered among our experiments, we shall find the metals 
falling into the analytical groups. If the student has 
made the experiments he will find it an interesting and 
profitable exercise to deduce this classification from them. 

To do this make a table, with six columns, like the 
blank form below, and then fill the blank spaces opposite 
the numbers in each column, by consulting the record of 
the results obtained by the experiments with the metals, 
thus : 



CHLORIDES 

insoluble in 
acid water. 


SULPHIDES 

insoluble in 
acid water. 


HYDROXIDES 

insoluble in 

NH 4 HO, 

andNH 4 Cl. 


SULPHIDES 

insoluble in 
NH 4 HO. 


CARBONATES 

insoluble in 

XH 4 HO, 

and N H 4 CI. 


1 

ALL SALTS 

soluble. 


1 

2 

3 


1 

2 

3 

4 

5 

6 

7 


1 

2 

3 


1 

o 

3 

4 


1 

2. 

3 


1 

2 ; 

3. . . . . J 
4 


Group I. 

precipitated 

by H CI. 


Group II. 

precipitated 

byH 2 S. 


Group III. 
precipitated 
by NH 4 HO. 


Group IV. 

precipitated 
by(XH 4 ) 2 S. 


Group V. 
precipitated 
by (NH 4 ) 2 
CQ 3 . 


1 

Group VI. | 
not precipi- 
tated. 



Place in the first column a list of all the metals which 
will give a precipitate with hydrochloric acid: you find 
their names by looking back over the experiments under 



270 CLASSIFICA TION. 

each metal. This list will contain the metals whose 
chlorides are insoluble in acid water. These metals make 
up Group I. 

Place in the second column a list of all the other metals 
whose sulphides are insoluble in acid water. These will 
make Group II. 

Place in the third, a list of all metals not found in 
the first and second columns whose hydroxides are not 
soluble in N H 4 H 0, or N H 4 CI. In this way we make 
out Group III. 

Place in the fourth, a list of all the metals not found 
in the first three columns, whose sulphides are insoluble 
in NH 4 H 0. These are the metals of Group IV. 

Place in the fifth, all the remaining metals whose 
carbonates are insoluble in 1ST H 4 H 0, or N H 4 CI. These 
are the metals in Group V. 

Place in the sixth, all the remaining metals whose 
chlorides, sulphides, hydroxides, and carbonates are all 
soluble. These are the metals in Group VI. 

We now find that our study of the metals, by experi- 
ment, has not only given us the facts about them and 
their compounds, but that it has also given us a way to 
detect their presence in substances whose composition is 
unknown to us. In fact, we are now prepared to analyze 
a salt, thus : — 

To find out what Metal a Salt contains. — If the 
salt is in the solid form we begin by making a solution 
of it. Then, — 

1. — Taking a small quantity of the solution in a 
tube, we add hydrochloric acid drop by drop. If a pre- 
cipitate is made in this way, it shows that the metal of 
the salt is one or another of the three in Group I. And 
then, to learn which one of these it is, we may try, with 
the solution, the experiments which are given under the 



CLASSIFICA TIOX. 271 

head of each of these particular metals, in our previous 
study of them. 

But if the hydrochloric acid yields no precipitate, we 
may say that the salt is not a compound of any one of 
these three metals, and may seek further, to find whether 
it is one of the seven metals of Group II. 

2. — The question is, whether its sulphide is insoluble 
in acid water. And to answer it, we take a little of the 
solution, make it acid by adding a drop or two of hydro- 
chloric acid, and then add hydrogen sulphide, H 2 S. If 
a precipitate is made in this way, our salt is a com- 
pound of one of the seven metals of Group II., but if 
none, it is not. 

Now the sulphides of three of these seven metals can 
be dissolved by ammonium sulphide (N H 4 ) 2 S, while those 
of the other four cannot. So we may take a little of 
our precipitate, and warm it with ammonium sulphide, 
and, if it proves to be soluble, we may say that the metal 
in our salt is one of these three, but if insoluble, we say 
that it is one of the other four. 

In either case we may find out which particular one 
of the metals is present, by making the experiments given 
in this book in the description of each of them. 

But if hydrogen sulphide has given no precipitate, we 
say that our salt is not a compound of any one of these 
seven metals, and go on to learn whether it is of one of 
the three in Group III. 

3. — The question now is, whether its hydroxide is 
insoluble in ammonia and ammonium chloride. And to 
answer this, we take a little of our first solution, put into 
it, first a considerable quantity of ammonium chloride, 
N H 4 CI, and then add ammonia, NH 4 HO, until the liquid 
smells strongly of this substance. It must be well shaken 
and the air blown out of the tube, then the odor of ammo- 



2 72 CLASSIFICA TION. 

nia will show when enough has been added. If a precipi- 
tate is made in this way, we may say that our salt is a 
compound of one of the three metals in Group III. And 
then, to know which one, we note the color of our precipi- 
tate and also make the experiments already described in 
the study of these three metals. 

But if we get no precipitate, we say that our salt cannot 
be a compound of any one of these metals. 

4. — The next question is, whether the sulphide of the 
metal we are after is insoluble in ammonia water. And 
to answer this, we take a little of our first solution, and put 
a little ammonia with it, then add ammonium sulphide 
drop by drop. A precipitate now shows that our salt is 
a compound of one of the four metals in Group IV. We 
then decide which one of the four, by noting the color of 
the sulphide, and also making the experiments given in 
our description of these metals. 

No precipitate here, with ammonium sulphide, proves 
that no one of these four metals is present in our salt. 

5. — We next ask, whether the carbonate of our metal 
is insoluble in ammonia and ammonium chloride, for if 
it is, then our metal is one of the four in Group V. 

To a little of the solution of our salt we add consid- 
erable ammonium chloride, NH 4 C1, and then add ammo- 
nium carbonate (NH 4 ) 2 C0 3 . If we get a precipitate, we 
next decide which one of the four metals of Group V. is 
present in our salt, by the experiments already given in 
the study of these metals. 

But if no precipitate is made, these four metals are 
thrown out of the question, and our salt must then be a 
compound of one of the metals in Group VI. 

6. — Which one of these four is it ? This is the final 
question. To answer it, we may make the experiments 
which are given in the descriptions of these metals, and 
see with which of the four our results agree. 



CLASSIFICATION. 273 

By following the order of the groups in this regular 
way, one can bring out the metal of almost any simple 
salt, with certainty and very quickly. 

The student may do this with a few simple salts whose 
names he does not know. The teacher will select them 
and keep a record of their names, and at the end of 
his work the student should report his work and the 
result of it. He should write down, in a short way, 
every experiment he makes, and Avhat the result of it 
is, and what it proves; and he should do this for each 
experiment, at the time he makes it, and not wait until 
others are made. 

On page 275 is a copy of one report of an " analysis/' 
which shows a form of the notes to be kept in each case. 
Notice that, below the heading, which is the name of 
the student, date of the work, and number of the sub- 
stance, the sheet is divided into three columns. In one, 
is put a brief description of all the experiments made. 
In the second, the result of each is written, and in the 
third, the fact which it proves. 

To find out what Acid the Salt contains. — But 
when we have found the metal in a salt, we do not 
yet know the name of the salt. It may be a nitrate, a 
chloride, or some other compound. The next step is to 
identify the acid part of it. This is done by making 
the tests which were described in our study of the non- 
metals, or the experiments described in the Exercises. 
Thus a test for sulphuric acid is given on p. 167, and 
the use of it, to show whether a substance is a sulphate, 
is illustrated in Ex. 122. See also the Exercises, p. 173. 
Hydrochloric acid, or its salts, — the chlorides, — may be 
identified by the test on p. 147. See also the exercises on 
p. 151. Nitric acid, and the nitrates also, may be detected 
by the " Copperas Test," p. 100. If a salt is a carbonate 



2 74 CLASSIFICA TION. 

it will effervesce when treated with dilute acid, and the 
gas which is set free will whiten lime-water. 

In this work for the acid, as in that for the metal, 
brief notes of all the experiments should be made, and re- 
ported. 

To Name the Salt. — Having found what metal a salt 
contains, and also what the acid part of it is, you can de- 
clare the name of the salt which was given you for analysis 
(p. 136). For example, having found strontium and nitric 
acid, the substance itself must be strontium nitrate. 

In this way, a "simple" salt, that is, a salt which 
contains only one acid and one metal, may be analyzed. 
The work is a most valuable exercise for the student at 
this stage of his progress, and, with a good reference book 
at hand, it should be carried as far as time will permit. 

Hint as to further Work. — Even " complex " sub- 
stances, that is, substances which contain more than one 
metal or acid, may be analyzed by very natural additions to 
the foregoing work. If, for example, we have a mixture 
of, say, silver and copper nitrates, we can detect both the 
silver and the copper. For we can separate them by using 
H CI, as was done in Ex. 195. 

If our mixture should contain one metal of every group, 
still every one of them could be "separated," and then 
" identified," by just such work. In such a case we could 
use the group reagents (see bottom of table, p. 269) one 
after another, in regular order. H CI would take out all 
of the metal of Group I., and leave all the others in solu- 
tion. Every group reagent in its order would precipitate 
all of the metal of its group, and leave all those of groups 
that come after in solution. In this way we should get 
each metal alone, and could then identify it. Of course, 
if a group reagent gives no precipitate, all metals of its 
group must be absent. 



CLASSIFICA TION. 
REPORT OF AN ANALYSIS. 

Name Date. 

Substance No. 



275 



EXPERIMENTS. 



RESULTS. 



INFERENCES. 



I. AdddropsofHCl. 



II. Tol. addH 2 S. 



III. To the original 
solution add NH 4 C1 
andNH 4 HO. 

IY. To III. add 
(NH 4 ) 2 S. 



Y. To original solu- 
tion add NH 4 C1 
and(NH 4 ) 2 C0 3 . 



VI. To the original 
solution add solu- 
tion of Ca S 4 . 

VII. Heat VI. to boil- 
ing. 

VIII. Flame-test. 



No precipitate made 



No precipitate made 



No precipitate made 



No precipitate made 



A ^svhite precipitate 



No precipitate made 
in the cold 



A white precipitate 



Brilliant crimson 



« 



Absence of Group I. 
Ag, Hg (ous), and 
Pb. 

Absence of Group II. 
■Hg(ic),Bi,Cu,Cd, 

As, Sb, Sn. 

Absence of Group 

III. Fe, Al, Cr, 

Absence of Group 

IV. Mn, Zn, Ni, 
Co. 

Presence of Group V. 
Ba, Sr, or Ca. 

Absence of Ba. 



Presence of Sr. 



Confirms presence 
of Sr. 



Hence substance No. is a compound of strontium. 



APPENDIX. 



THE APPARATUS. 

The following list contains the pieces in a single set of ap- 
paratus for the course of experiments described in this book. 
The full set is shown in the cut, Fig. 69. It is designed for 
the use of beginners, unused to manipulation, and of teachers 
who are oftentimes so pressed by other duties that little time 
remains for the preparation of experiments. Selected from the 
standard articles in the outfit of the chemist, they are neat 
in appearance, efficient in action, easily put together, and 
comparatively cheap. The forms shown in the cut are of the 
pieces which have been actually used in devising and testing 
the experiments described. 

Fragile articles, such as test-tubes and flasks, should be 
bought in quantity, to allow for breakage. One balance will 
serve several workers. The same is true of the thermometer, 
where economy must be practiced, and a single graduated 
cylinder for each will do very well, although in that case all 
cannot, at one time, make Ex. 37. 

The pieces are here described in the order of their numbers 
in the cut. 

1. Graduated Cylinder. — A tall and narrow glass 
cylinder on foot, about f inches in diameter, 25 cc. graduated 
to halves. 

Number required in single set 2 

2. Test-tubes and Rack. — Tubes 6 inches long by f 
inch in diameter. They should be bought by the gross. The 
rack to support the tubes can be made by any carpenter. Its 
form is shown in the cuts. 

Number required in single set 12 

279 



280 APPENDIX. 

3. Side-neck tube. — Of German or soft glass, and of 
Bohemian or hard glass, G x f inches. They may be bought 
by the dozen, and kept in stock. 

Number required in single set, of soft glass . . 1 

" hard ; ' . . . 1 

4. Mortar and Pestle. — Of glass or porcelain, glazed 
inside and outside, 3J inches diameter. 

5. Support with Ring and Clamp. — The support is 
of iron. It is the so-called retort-stand. We select the small 
size, usually provided with two rings. Only one ring is called 
for, but the second will be found useful. These rings should 
be arranged, as shown, to be taken off at the side of the rod. 
The clamp is " small size " with " universal movement," to hold 
a tube or flask in horizontal or vertical or oblique position. 

6. Side-neck Flask. — A round bottom flask with a side 
neck attached to the stem. 

Number required for each student's set, 150 cc. . 1 
11 " " the teacher's set, 150 cc. . 1 

and 250 cc. . 1 

7. Conical Flasks. — The so-called Erlenmeyer flasks, 
or Beaker flasks. These are thin and rather fragile, but with 
care will last a long time. Their freedom from color, perfect 
transparency, uniformity in shape and size, render them 
peculiarly well fitted for the examination of gases and liquids. 
Flasks of the usual form, or bottles, may be used instead of 
these, and, if made of white glass, and have mouths of uniform 
size, to be perfectly closed by the stoppers, bottles are very good 
and more durable. The mouth should be f to 1 inch in diam- 
eter, taking a No. 4 or No. 5 E. & A. soft rubber stopper. 

The use of these flasks and bottles, as described, for collect- 
ing and examining gases, dispenses with the pneumatic cistern, 
and the unpleasant wetness which goes with it. This method 
also enables one to dispose of noxious substances with gratify- 
ing success. 

For each student 200 cc. or 8 oz. flasks 4 

For the teacher, 200 cc. or 8 oz. flasks 2 

400 cc. or 16 oz. flasks .... 4 



APPENDIX. 281 

8,9. Rubber stoppers. — Success in managing gases 
by this method demands that all joints in the apparatus shall 
he air-tight. Such joints are easily made by means of rubber 
stoppers No. 9, arranged with glass tubes No. 8. Each flask or 
bottle is to be supplied with this arrangement, and they are then 
to be joined together by rubber tubing. The first cost of rubber 
stoppers is larger than of cork, but their durability is a compen- 
sation. They should be of the "best soft rubber," and of such 
sizes as to fit the mouths of the flasks and tubes in use. Their 
sizes are described by numbers, but the same number, used 
by different makers, does not always describe the same size or 
quality. To be definite, we now refer to those stamped " E. 
& A." (Eimer and Amend). 

No. 3 will fit a f- inch tube or flask or bottle. 
No. 4 " " i " flask or bottle. 
No. 5 " " 1 " " bottle. 

One "solid "will be needed, to close the side-neck tube or 
flask ; one " with two holes," to close each flask or bottle in 
use. 

10. Bunsen Burner. — In laboratories not supplied 
with gas, the alcohol lamp is the best substitute. 

11. Glass Funnel. — The best German make, with long 
thin stem. Diameter 2 J inches. 

12. Wide-mouth Bottles. — Flint glass, tall style. 

Bottles should be bought by the dozen, or in larger labora- 
tories by the gross. 

Needed for each set, wide-mouth, 200 cc. or 8 oz. . 1 

extra wide-mouth, 200 cc. " " . 1 

wide-moutb, 400 cc. " 16 oz. 1 

13. Forceps. — Steel, plain, 4£ inches. 

14. Glass tubing. — Made of the best German or soft 
glass. It should be of such size as to fit the holes in the rubber 
stoppers used, about ^ inch outside diameter for those de- 
scribed above. It may be cut into pieces, of any length desired, 
by first drawing across it the edge of a sharp three-cornered 



282 APPENDIX. 

file, once, making a distinct scratch, and then pulling the tube, 
almost but not quite lengthwise. The sharp cut edges may 
be rounded by heating them until red in the lamp-flame. 
Glass tubing is to be bought by the pound. 

15. Porcelain Dish. — So-called "evaporating dish." 
The R. B. porcelain is best. Diameter 3J inches. 

These may be bought by the dozen. 

Needed for each set 1 or 2 

16. Drying Tube. —The so-called "chloride of calcium 
tube," with one bulb, length 5 inches. 

17. Pinch-cock. — Mohr's, small size, strong. 

18. The Balance. — A balance of good quality is the 
most costly piece in the outfit for laboratory work. In quali- 
tative chemistry, such as the foregoing course, it is not abso- 
lutely indispensable, because something can be done by means 
of cheap substitutes, — even by such as an ingenious student 
can make. 

The balance shown in the cut is a Becker's balance, listed 
in "Becker Brothers" catalogue as No. 14, at $11.00. With a 
glass case, which is very desirable to protect the instrument 
from dirt and corrosion, it is listed as No. 16, at $ 22.00. It is 
neat, accurate, sensitive to 2 mg., and durable. 

The weights for this balance should be a set of 50 g. to 1 g. 
in brass, and 500 mg. to 1 mg. in platinum or aluminum 
with forceps, all in a lined and covered box. Such a set is 
listed by Becker Brothers at $9.00, and by Eimer and Amend 
at $5.50. 

From parties (John Wannamaker, Philadelphia) who im- 
port from Becker's Sons of Eotterdam, the balance and weights 
just described, or their equivalent, can be obtained by schools, 
free of duty, at much less cost. 

19. The Water Pan. — A pan about 8 inches diameter, 
and 3 or 4 inches deep, with fiat bottom and straight walls. 
It may be of glass — a so-called crystallizing dish, as shown in 
the cut, or it may be of agate-iron ware, which is likely to be 
more durable, but less shapely. 



APPENDIX. 283 

20. A common Plate. — A small size china plate. 

21. Rubber Tubing. — To connect the Bnnsen Burner 
with the gas supply, white rubber, thick, i inch diameter inside, 
may be used. Ked rubber is better, and a little more costly. 

For joining parts of the gas-apparatus the black or red 
tubing, of usual thickness, is to be preferred. The size should 
correspond with that of the glass tubing, which it must fit. 
Rubber tubing is bought by the foot. In pieces of 12 feet it 
comes a little cheaper. 

22. A Chemical Thermometer. — A Centigrade ther- 
mometer, graduated from about — 20° to + 200°. The best in- 
strument has its scale on the glass stem itself. A cheaper and 
very good instrument has a paper scale enclosed in a glass 
tube, which protects the stem. 



THE CHEMICALS. 

In the following list may be found the names and formulas 
of all the substances required to make the experiments de- 
scribed in this book. Chemicals, to be used in the study of 
chemistry, should be of the best quality. Many of those fur- 
nished by the shops are impure, and often lead to wrong and 
troublesome results. It is better to buy chemicals, as you buy 
apparatus, from well-known dealers in laboratory supplies. 

Eeagents, which are to be used by students, should be kept 
upon their tables in small bottles : liquids in glass-stoppered 
bottles holding about 125 cc. or four oz., and solids in salt-mouth 
bottles holding 2 oz. If substances are to be used by the 
teacher they may, for the most part, be kept in the bottles in 
which they are bought. Every bottle should be distinctly and 
permanently labelled. 

Unless economy must be rigidly practiced, the supply will not 
be limited to the substances in this list; specimens, in great 
variety, are very desirable. 

The author will gladly give any information he can in regard 
to the purchase or use of apparatus and chemicals. 



Acetic acid, pure . . 


. H C 2 H 3 2 


Alcohol .... 


. C 2 H 6 


Alum . .... 


. K 2 A1 2 (S0 4 ) 4 + 24H 2 


Ammonium carbonate, C. P. 


. (NH 4 ) 2 C0 3 


chloride, C P. 


. NH 4 C1 


hydrate 


N H 4 H 


" nitrate, cryst. 


. NH 4 Jsro 3 


Antimony chloride, sol. C. P. 


Sb Cl 3 


Arsenous oxide .... 


■ As 2 3 


Barium chloride, C. P. . 


Ba Cl 2 


284 





APPENDIX. 


Bismuth nitrate, cryst. C. P. 


. Bi(N0 3 ) 3 


Bone-black .... 


C 


Bromine 


. Br 


Calcium chloride, crude 


Ca Cl 2 


cryst. C. P. . 


. 


" oxide (quicklime) . 


CaO 


Carbon pencil .... 


. C 


Chrome alum 


• K 2 Cr 2 (S0 4 ) 4 


Cobalt nitrate, C. P. . 


. Co(X0 3 ) 2 


Cochineal .... 




Copper, thin sheet 


. Cu 


" chloride . 


Cu Cl 2 


" sulphate, C P. 


. CuS0 4 


Dutch metal (imitation gold-lea 


i) Cu Zn 


Ferrous sulphate, pure 


. FeS0 4 


" sulphide (sticks) 


FeS 


Hydrochloric acid, pure 


. HC1 


Iodine 


I 


Lead acetate .... 


. Pb(C 2 H 3 2 ) 2 


Litmus (blocks) 




Logwood 




Magnesium (ribbon) 


. Mg 


" chloride, cryst. 


. MgCl 2 


sulphate, C. P. . 


Mg S 4 


Manganese dioxide, powder 


. Mn0 2 


" sulphate 


Mn S 4 


Marble 


. Ca C 3 


Mercury, redistilled 


■ Hg 


Mercuric chloride (cor. sub.) 


. HgCl 2 


" oxide 


. HgO 


Nickel chloride .... 


. MC1 2 


Nitric acid, pure . 


HN0 3 


Oxalic acid, C. P. 


. H 2 C 2 4 


Parafhne .... 


L n -ti 2n 2 


Phosphorus .... 


. P 


Potassium .... 


K 


bromide, C. P. . 


. KBr 


tl carbonate, C. P. . 


K 2 C0 3 



285 



+ 24 H 2 



286 



APPENDIX. 



Potassium chlorate, cryst. 
" chromate 
" dichromate 
" ferrocyanide 
" hydrate, pure 
iodide, C. P. . 
" nitrate, cryst. 
" sulphate, cryst. 
Platinum foil 

" wire 
Pyrogallic acid . 
Silver nitrate, cryst. 
Sodium 

" biborate (borax) 
" carbonate, C. P. 
hydrate, C. P. . 
" nitrate . 
" sulphate . 
Strontium chloride . 

" nitrate, C. P. 
Sulphur, flowers 

roll . 
Sulphuric acid, pure . 
Tartaric acid, cryst. 
Tin (granulated) 
Zinc (sheet) . 

" (granulated) . 
Sugar (granulated) 
Salt .... 
Charcoal . . ■ . 



KCIO3 

K 2 Cr 6 4 

Jv 2 Cr 2 7 

K 4 FeCy 6 

KHO 

KI 

KXO3 

K 2 S0 4 

Pt 

Pt 

C 6 H,(HO) 3 

AgN0 8 

Na 

Na 2 B 4 7 + 10 H 2 O 

Na 2 C 3 

Na H 

Na N 3 

Na 2 S 4 

Sr Cl 2 

Sr(N0 3 ) 2 

S 

s 

H 2 S0 4 
C 4 H 6 6 

Sn 
Zn 
Zn 

^12 ^22 ^11 

NaCl 

C 



METRIC AND ENGLISH MEASURES. 



Measures of Weight 

10 milligrams, nig. = 1 centigram, eg. = 



10 centigrams, eg. 
10 decigrams, dg. 
10 grams 
10 decagrams 
10 hectograms 



= 1 decigram, dg. = 

= 1 GRAM, g. = 

= 1 decagram = 
= 1 hectogram = 
= 1 kilogram = 



0.154 grains. 
1.543 grains. 
15.432 grains. 
154.323 grains. 
3.527 oz. avoir. 
2.204 lb. avoir. 



APPENDIX. 2S7 

1 grain = 0.0648 g. or 64.799 mg. 

1 oz. Troy = 31.1035 g. 1 oz. avoir. = 28.349 g. 

. 1 lb. Troy = -3700 grains. 1 lb. avoir. = 7000 grains. 

Measures of Volume. 

10 cubic centimeters, cc. = 1 centiliter, cl. = 0.338 fid. oz. 

10 centiliters = 1 deciliter = 0.845 gill. 

10 deciliters = 1 liter, 1. = 1.057 quart. 

10 liters = 1 decaliter = 2.642 gal. 

10 decaliters = 1 hectoliters, hi = 26.417 gal. 

10 hectoliters = 1 kiloliter = 264.18 gal. 

1 cu. in. = 16.386 cc. 1 U S. quart = 0.9469 1. 

1 liter = 61.027 cu. in. 1 U. S. gal. = 3.785 1. 

1 U. S. gal. = 231 cu. in. 1 Imp. gal. = 277.25 cu. in. 

Measures of Length. 

10 millimeters, mm. = 1 centimeter, cm. = 0.3937 in. 
10 centimeters = 1 decimeter = 3.937 in. 

10 decimeters = 1 meter, m. — 39.37 in. 

10 meters = 1 decameter = 32.8 ft. 

10 decameters = 1 hectometer = 328.08 ft. 

10 hectometers = 1 kilometer, km. = 0.62137 mile. 

1 inch = 2.534 cm. 1 millimeter = 0.0393 in. 

1 yard = 0.9144 m. 1 meter = 1.0936 yd. 

1 mile = 1.6093 km. 1 kilometer = about | mile. 

Measures of Temperature. 

Freezing-point of water = 0° Centigrade, C. or 32 : Fahrenheit, F. 
Boiling-point of water — 100° " or 212- 

lo c. = §° or 1.8° F. 1° F. = f°, or 0.555° C. 

To change a Centigrade temperature to its equivalent Fahren- 
heit temperature: Multiply by § and add S'2 Z to the product. 

To change a Fahrenheit temperature to its equivalent Centi- 
grade temperature : Subtract 32 and multiply the remainder 
by f. 



INDEX. 



THE NUMBERS REFER TO PAGES. 



Absorption, analysis by, 70, 82. 

of gases by charcoal, 106. 

of gases by water, 59, 86, 146. 

of hydrogen by palladium, 261. 
Acid-forming elements, 192, 236. 
Acids, 129. 

action of, on bases, 133. 

action of, on metals, 134. 

chief characteristic, 130. 

classes of, 130. 

dibasic, 172. 

monobasic, 173. 

names of, 135. 
Acid salts, 173. 
Agate, 184. 
Air spoiled by breathing, 79. 

analysis of, 69-74. 

in water, 59. 
Alkalies, metals of, 204. 
Allotropism, 39. 
Alloys, 214. 

of antimony, 235. 

of bismuth, 235. 

of copper, 248. 

of gold, 260. 

of mercury, 251. 

of osmium, 261. 

of silver, 256. 
Alum, 233. 

ammonium, 233. 

chrome, 230. 



Alumina, 233. 
Alluminum, 233. 

compounds of, 233. 

compounds in dyeing, 234. 

hydroxide, 234. 

oxide, 233. 

reactions of, 234. 

sulphide, 234. 
Amalgams, 251. 
Amalgamated zinc, 26. 
Amalgamation in metallurgy, 255, 

259. 
Amethyst, oriental, 233. 

quartz, 183. 
Amine, 182. 
Ammonia, 84-90. 

absorbed by charcoal, 106. 

absorbed by water, 86, 88. 

composition of, 90. 

in food of plants, 102. 

in air, 69, 85. 

Nessler's test for, 99. 

preparation of, 85. 

solubility of, 88. 

sources of, 84, 85. 
Ammonium, 201-204. 

alum, 233. 

a metal, 202. 

chloride, 19. 

disulphide, 203. 

hydrate, 87. 



290 



INDEX. 



Ammonium, hydrosulphide, 203. 

reactions of, 203. 

salts, 88, 202. 

sulphides, 160, 203. 
Analysis, denned, 24, 50. 

by absorption, 70, 82. 

by electricity, 51. 

grouping for, 269. 

notes of work in, 273, 275. 

of air, 69-74. 

of a metallic salt, 270-275. 

of a complex salt, 274. 

of a simple salt, 274. 

of unknown substances, 270. 

of water, 50-55. 

report of an, 275. 

systematic, 268. 
Anhydride, defined, 165. 

arsenic, 180. 

arsenous, 179. 

carbonic, 184. 

phosphoric, 177. 

phosphorus, 177. 

silicic, 184. 

sulphuric, 169. 

sulphurous, 165. 
Animal charcoal, 108. 
Antimonetted hydrogen (stibine), 

235. 
Antimony, 235. 

alloys of, 235. 

compound with hydrogen, 235. 

group, 236. 

ores of, 235. 

reactions of, 237. 

related to non-metals, 235. 

sulphide, 237. 
Apparatus for this course, 279. 
Aqua regia, 92, 143, 260. 
Arsenuretted hydrogen (arsine), 
180. 



Arsenic, 178-182. 

acid, 180. 

Marsh's test for, 181. 

native, 179. 

oxides, 179, 180. 

reactions of, 237. 

related to metals, 236. 

sulphide, 237. 

white, 179. 
Arsenous oxide, 179. 
Arsenical pyrites, 179. 
Arsenites, 180. 
Arsine, 182. 
Atmosphere, chemistry of, 65-83. 

a mixture, 74. 

analysis of, 69. 

composition of, 73, 75. 

constituents in, 69. 
Atomic theory, 123. 

weights, 118, 124. 
Atomic weights and properties, 

facts from the CI. group, 151. 

facts from the S. group, 162. 

facts from the N. group, 182. 

facts from the Ca. group, 210. 

facts from the Zn. group, 216. 

facts from the Fe. group, 231. 

Newland's discovery, 264. 

MendelejefPs system, 266. 

shown in spiral form, 267. 

suggests new elements, 268. 
Atoms, 122. 
Avogadro's law, 122. 

Baking Powders, 200. 
Baking soda, 40, 200. 
Barium, 210. 

reactions of, 211. 
Base-forming elements, 192. 
Bases, defined, 133. 

action on acids, 133. 



INDEX. 



291 



Bases, names of, 136. 

Basic salts, 245. 

Battery, voltaic, 51. 

Bell-metal, 248. 

Bessemer process for steel, 226. 

Bismuth, 235. 

reactions of, 237. 

related to non-metals, 236. 

sulphide, 237. 
Black-ash, 200. 
Black-lead, 110. 

Black oxide of manganese, 217. 
Blast-furnace, 221. 
Bleaching, by chlorine, 140. 

by sulphurous oxide, 165, 166. 

powder, 141, 208. 
Blende zinc, 212. 
Blistered steel, 226. 
Bloodstone, 183. 
Boiling-point, 61. 
Bone-ash, 178. 
Borax, 185. 
Boric acid, 186. 
Boron, 185. 

valence of, 190. 
Brass, 214, 248. 
Brimstone, 155. 
Bromides, 148. 

reactions of, 151. 
Bromine, 148. 
Bronze, 248. 
Bunsen burner, 10, 47. 

Cadmium, 215. 
Csesium, 204. 
Calamine, 212. 
Calcium, 206-211. 

carbonate, 206-208. 

chloride, 86, 207. 

flame color of, 211. 

group, 210. 



Calcium hydroxide (slaked lime), 
207. 

hypochlorite, 208. 

insoluble compounds of, 208. 

occurrence, 206. 

oxide (quick-lime), 206. 

phosphate, 178. 

reactions of, 211. 

soluble compounds of, 210. 

sulphate, 208, 210. 
Calcium carbonate, 113, 206. 

decomposed by acids, 207. 

decomposed by heat, 206. 

dissolved by water, 208. 

precipitated, 113. 
Calomel, 252. 
Calorie, 32. 
Carbon, 103-112. 

alio tropic forms of, 111. 

compounds with hydrogen, 
115. 

constituent of plants, 101. 

diamond, 109. 

dioxide, 112. 

from sugar, 12. 

graphite, 110. 

group, 184. 

lamp-black, 105. 

manufacture of charcoal, 104. 

monoxide, 115. 

source of, in plants, 103. 
Carbonates, 184. 

basic, 245, 248. 
Carbon dioxide, 112-114. 

absorbed by plants, 81. 

a constituent of air, 74. 

by burning charcoal, 18. 

preparation of, 112. 

properties of, 113. 

product of combustion, 42. 

product of respiration, 78. 



292 



INDEX. 



Carbon, synthesis of, 36. 

test for, 17, 36, 113. 
Carbon monoxide, 82, 115. 
Carbonic acid, 184. 

anhydride, 184. 
Carnelian, 184. 
Cast-iron, 222. 
Catalysis, 35. 
Caustic potash, 197. 
Caustic soda, 200. 
Cementation, 226. 
Chalcedony, 184. 
Changes, of two kinds, 14. 
Charcoal, 105. 

action of, on colors, 108. 

action of, on gases, 106. 

action of, on oxides, 109. 

a disinfectant, 107. 

animal, 108. 

combustion of, 36. 
Chemical change, 13-40. 

a change in molecules, 122. 

agents to produce, 28. 

a source of electricity, 25. 

a source of heat, 25. 

a source of light, 27. 

combination, 17. 

decomposition, 14. 

double decomposition, 21. 

exercises in, 39. 

substitution, 19. 
Chemical calculations, 127. 
Chemical names, 135. 
Chemicals for this course, 284. 
Chemistry, how to study, 9, 12. 
Chilian saltpetre, 90. 
Chlorides, 141-147. 

hydrogen-chloride, 145. 

preparation of, by aqua regia, 
92. 

preparation of, by chlorine gas, 
141. 



Chlorides, preparation of, by chlo- 
rine water, 142. 

preparation of, by hydrochloric 
acid, 142. 

reactions of, 151. 

test for, 147. 

two, of one metal, 144. 
Chlorine, 138-147. 

action of, on metals, 140, 141, 

a disinfectant, 140. 

bleaching by, 140. 

group, 147. 

preparation of, 138. 

properties of, 139. 

test for, 147. 
Chlorine group, 147-153. 

general behavior, 151. 

hydrogen compounds of, 150. 

members of, described, 148, 149. 

properties and atomic weights 
of, 151. 

reactions of, 151-153. 
Choke-damp, 114. 
Chrome alum, 230. 

yellow, 230. 
Chromic iron (chromite), 229. 
Chromite, 229. 
Chromium, 229. 

compounds of, 230. 

reactions of, 230. 
Chrysoprase, 183. 
Cinnabar, 251. 
Classes, how made, 262. 
Classification, 262-275. 

analytical, of metals, 268. 

a natural system, 264. 

in a spiral form, 266. 

Mendelejeff's table, 266. 

metals and non-metals, 236, 262. 

of metals, 262. 

of non-metals, 261. 
Clay, 233. 



INDEX. 



293 



Clay-iron stone, 221. 
Coal, 105. 
Cobalt, 220. 

" fly-poison," 178. 
Coin, analysis of, 257. 

gold, 260. 

silver, 256. 
Combination, 17. 

by volume, 55, 146, 147. 

law of, by volume, 147. 

law of constant proportions, 
57. 

law of multiple proportions, 
97, 123. 
Combining weights, 98. 
Combustion, 37, 41-49. 

a mutual action, 42. 

imperfect, 42. 

of hydrogen and oxygen, 43. 

produces heat, 43. 

produces light, 46, 49. 

produces compounds, 42. 
Complex salts, 274. 
Compounds denned, 24. 

differ from elements, 122. 

formulas of, 124. 

neutral, 134. 
Constituent, 24. 
Copper, 247-251. 

alloys of, 248. 

arsenite, 180. 

carbonate, 248. 

chloride, 141, 250. 

compounds of, 248. 

extraction of, 248. 

hydroxide, 250. 

native, 247. 

ores of, 247. 

oxides, 249. 

pyrites, 247. 

reactions of, 249. 



Copper sulphate, 171, 249. 

sulphide, 157, 250. 
Copperas, 100. 
Cork-borers, 31. 
Corrosive sublimate, 252. 
Cupellation, 255, 256. 
Cupric compounds, 249. 
Cuprous compounds, 249. 

Decomposition, 14. 
Definite proportions, law of, 57. 
Deliquescence, 197. 
Diamond, 109. 
Dibasic acids, 172. 
Diffusion of gases, 75. 
Dimorphism, 157. 
Disinfectants, 107, 140, 214, 217. 
Distillation, 60. 

fractional, 64. 
Drinking-water, 59. 
Dutch metal, 139, 141. 

Effervescence, 207. 

Electricity and chemical action, 25. 

decomposition by, 26, 51-54. 

produces ozone, 38. 
Element defined, 24. 

differs from compound, 122. 
Elements, ancient, 41. 

atomic weights of, 118, 123, 
124. 

classification of, 262. 

number of, 117. 

symbols of, 118, 123. 

table of, 118. 
Emerald, 233. 

English and French measures, 286. 
Epsom salt, 212. 
Equations, chemical, 127. 
Etching glass, 150. 
Evaporation, 20. 



294 



INDEX. 



Exercises in investigation, 39, 63, 

82, 98. 
Experiment, defined, 10. 
value in chemistry, 12. 

Ferric chloride, 144. 

Ferrous chloride, 144. 

Ferrous and ferric compounds, 226. 

Filter, 20. 

Filtration, 20. 

Fire, 41. 

Fire-damp, 116. 

Flame, due to gas, 45. 

effect of cooling, 49. 

oxyhydrogen, 43. 

smoke of, 42. 

source of the light, 47. 

structure of, 48. 

tests, 198, 201, 211. 
Flame color, to produce, 198. 
Flint, 183. 

Flowers of sulphur, 155. 
Fluorine, 149. 
Fluor spar, 150. 
Fly powder, 178. 
Fool's gold, 154. 
Formulas of compounds, 124. 
Fractional distillation, 64. 
Freezing-point, 63. 
Fuel, 42. 

Furnace, 221, 223. 
Fusible metal, 235. 

Galena, 154, 242. 

Gallium, 268. 
Galvanized iron, 214. 
Gas, illuminating, 85. 
Gases, analysis of, 70, 82. 

burn with flame, 45. 

diffusion of, 75. 

expansion of, 121. 



Gases, measurement of, 71. 

method of drying, 31. 

method of collecting, 29, 33. 

solubility of, 59. 
German silver, 214, 248. 
Glass, 185, 208. 

blue, 220. 

hard and soft, 14. 
Gold, 259. 

coin, 260. 

extraction by washing, 259. 

extraction by amalgamation, 
259. 

properties of, 259. 
Graphite, 110. 
Green vitriol, 249. 
Groups, 262. 

analytical, 269. 

natural, 266, 267. 

of non-metals, 147, 161, 182, 184. 

of metals, 262-264. 
Grouping by atomic weights, 264. 

by likeness of properties, 263. 

by solubility of compounds, 
264, 268. 

by valence, 262. 

for analysis, 269. 
Gypsum, 208. 

Haematite, 221. 

Heat, agent in chemical change, 28. 

a product of chemical change, 
19, 25, 28. 

intensity of, 44. 

quantity of, 44. 

unit of, 32. 
Hydrates, 133. 
Hydrocarbons, 115. 
Hydrochloric acid, 145. 

composition of, 146. 

constant composition, 56. 



INDEX. 



295 



Hydrochloric acid, preparation of, 
145. 

properties of, 146. 

solubility of, 58, 59, 146. 
Hydrofluoric acid, 150. 
Hydrogen, 28-32. 

antimoiiide (stibine), 235. 

arsenide (arsine), 180. 

chloride, 145. 

diffusion, 75. 

explosibility, 30. 

in nature, 32. 

nitride (ammonia), 84-88. 

phosphide (phosphine), 182. 

preparation of, 19, 28. 

properties of, 29-32. 

set free by electricity, 26. 

solubility of, 59. 

sulphide, 158. 

weight of a liter, 32. 
Hydrogen sulphide, 158. 

preparation of, 159. 

properties of, 160. 

use of, 160. 
Hydroxides, 131. 

names of, 137. 
Hypophosphorus acid, 177. 

Ice, 63. 

Ignition tubes, 14. 
Illuminating gas, 85. 
Investigation of some chemical ac- 
tions, 39. 

in study of nitric acid, 92. 

of sulphuric acid on iron, 40. 

of H 2 S 4 on oxalic acid, 82. 

other examples of, 30, 63, 99, 
173. 
Iodides, 149. 

reactions of, 151. 
Iodine, 148. 



Iodine, test for, 149. 

tincture, of, 149. 
Iridium, 261. 
Iron, 220-232. 

chlorides, 144. 

combustion of, 36. 

compounds of, 226. 

extraction of, 221. 

galvanized, 214. 

group of metals, 217, 231. 

hydroxides, 137. 

manufacture of cast, 222. 

manufacture of steel, 225. 

manufacture of wrought, 223. 

occurrence of, 220. 

ores of, 220. 

reactions of, 226-229. 

sulphate, 170. 

sulphides, 158, 220. 

two classes of salts of, 226. 

Jasper, 183. 

KlNDLING-POlNT, 44. 

Laboratory Supplies, 279-284. 
Lamp-black, 105. 
Laughing-gas, 96. 
Lavoisier's experiment, 65. 
Law, 119. 

Avogadro's, 122. 

of constant proportions, 57. 

of multiple proportions, 97, 123. 

the periodic, 266. 

the " two volume," 147. 
Lead, 242-246. 

carbonate, 244. 

chloride, 245. 

chromate, 230. 

extraction of, 242, 243. 

iodide, 246. 

nitrate, 245. 



296 



INDEX. 



Lead, ores of, 242. 

oxides, 244. 

properties of, 244. 

reactions of, 245. 

sulphide, 245. 

symbol of, 242. 
Lead-tree, 243. 
Light, and chemical action, 27. 

of flames, 46. 

on nitric acid, 91. 

oxyhydrogen, 46. 
Lime, 206. 
Lime-light, 46. 
Limestone, 206. 
Lime-water, 207. 

a test for C0 2 , 17. 
Litharge, 244. 
Lithium, 204, 265. 
Lucifer match, 165. 

Magnesia, 212. 
Magnesium, 212. 

carbonate, 212. 

combustibility of, 13. 

oxide, 212. 

reactions of, 212. 

sulphate, 212. 
Magnetic oxide, 220. 
Malachite, 247. 
Malleable iron, 224. 
Manganese, 217. 

reactions of, 218. 
Marble, 206. 
Marsh-gas, 116, 184. 
Matches, 165, 176. 
Melting-point, 63. 
MendelejefPs system, 266. 
Metal, defined, 192. 
Metals, 192. 

and non-metals, 193, 236. 

analytical groups of, 269. 



Metals, classification of, 262, 264. 

native, 193. 

number of, 193. 

occurrence of, 193. 

of the alkalies, 204. 

of the alkaline earths, 210. 

the calcium group, 210. 

the copper group, 247. 

the iron group, 231. 

the platinum group, 261. 

the potassium group, 204. 

the zinc group, 215. 
Metallurgy, 194. 

amalgamation in, 255, 259. 

cupellation in, 255, 256. 

precipitation in, 243. 

reducing ores, 213. 

roasting ores, 213. 

washing of gold, 259. 
Meteoric stones, 220. 
Methane, 116, 184. 
Metric measures, 286. 
Mercury, 251-253. 

alloys of, 251. 

chlorides, 252. 

compounds of, 252, 253. 

extraction of, 251. 

ore of, 251. 

oxide, 14, 252. 

reactions of, 252. 

sulphide, 253. 
Mineral waters, 59. 
Mining, 194. 
Minium, 244. 
Mispickel, 179. 
Mixture defined, 24. 
Molecular weights, 125. 
Molecules, 121. 
Monobasic acids, 173. 
Mortar, 207. 
Multiple proportions, 97. 



INDEX. 



297 



Multiple proportions, law of, 97 
123. 

Nascent state, 85. 
Nessler's reagent, ,98. 
Neutral compounds, 134. 
Neutral salts, 173. 
Neutralization, 133. 
NewlancTs discovery, 264. 
Nickel, 219. 
Nitrates, 92. 

tests for, 100. 
Nitre, 196. 
Nitric acid, 90-95. 

decomposition of, 91, 92. 

preparation of, 91. 

properties of, 91. 

test for, 100. 
Nitric oxide, 95. 
Nitrogen, 66. 

compounds, 84. 

group, 182. 

in plants, 102. 

oxides, 92-96. 

properties of, 69. 
Non-metals, 192. 

classification of, 189, 262. 

the carbon group, 184. 

the chlorine group, 147. 

the nitrogen group, 182. 

the sulphur group, 161. 
Nomenclature, 135. 
Normal salts, 173. 

Observation, 9. 
Oil of vitriol, 166. 
Onyx, 184. 
Opal, 183. 
Ores, 194. 
Osmium, 261. 
Oxidation, 37. 
slow, 175. 



Oxides, 37. 

nitrogen, 96. 

reduction of, 109. 
Oxidizing agent, 217, 228. 
Oxygen, 33-39. 

allotropism of, 38. 

in nature, 37. 

preparation of, 14, 16, 33. 

solubility of, 59. 

test for, 34. 
Oxyhydrogen flame, 43. 

blowpipe, 43. 
Ozone, 38. 

Paris green, 180. 
Percentage composition, 55. 
Periodic law, 266. 
Phosphates, 178. 
Phosphine, 182. 
Phosphoric acid, 177. 
Phosphorous acid, 177. 
Phosphorus, 175-178. 

acids, 177. 

action on air, 83. 

allotropic forms, 176. 

burning of, 67, 68. 

manufacture of, 178. 

oxides, 177. 

properties of, 175. 

red, 175. 

salts of, 178. 
Phosphuretted hydrogen (phos- 
phine), 182. 
Photography, 173, 257. 
Pig-iron, 222. 
Plants, composition of, 101. 

food of, 102. 

respiration of, 81. 
Plaster of Paris, 208. 
Platinum, 260. 

group of metals, 261. 



298 



INDEX. 



Plumbago, 110. 
Potash, 196. 
Potassium, 196-198. 

action on water, 195. 

alum, 233. 

carbonate, 196. 

chlorate, 16, 35. 

chloride, 197. 

group of metals, 204. 

hydroxide, 196. 

manganate, 219. 

nitrate, 196, 197. 

occurrence of, 195. 

permanganate, 217, 219. 

reactions of, 197. 

tartrate, 197. 
Precipitate, 23, 198. 

when one will fall, 210. 
Precipitation in metallurgy, 243. 
Prussian blue, 228. 
Puddling, 223. 
Pyrites, arsenical, 179. 

copper, 247. 

iron, 154, 158, 220. 

Quartz, 183. 
Quick-lime, 206. 

Reactions, 126. 

numerical, 127. 

way to write, 127, 190. 
Red-lead, 244. 
Red phosphorus, 175. 
Report of analysis, 275. 
Respiration, 77. 

effect an air, 79. 

of plants, 81. 

products of, 78. 
Reverberatory furnace, 223. 
Rhodium, 261. 
Roasting of ores, 179, 213. 



Rock crystal, 183. 
Roll brimstone, 155. 
Rubidicem, 204. 
Ruby, 234. 
Ruthenium, 261.- 

Salt, defined, 131. 
common, 56. 
Salt-cake, 199. 
Saltpetre, 90, 196. 
Salts, 131. 

acid, 173. 

analysis of, 270-274. 

basic, 245. 

complex, 274. 

names of, 136, 274. 

preparation of, 131. 

preparation by fusion, 219. 

preparation by evaporation, 
210. 

preparation by precipitation, 
208. 
Sandstone, 183. 

simple, 274. 
Sapphire, 234. 
Selenides, 161. 
Selenium, 161. 
Silica, 183. 
Silicates, 184. 
Silicic acid, 184. 
Silicon, 183. 

hydride, 184. 

oxide, 183. 
Simple salts, 274. 
Silver, 254-258. 

chloride, 22, 27, 257. 

coin, 256. 

compounds of, 256. 

extraction from the sulphide, 
254. 

extraction from galena, 255. 



INDEX. 



299 



Silver, nitrate, 256. 

ores of, 254. 

properties of, 256. 

reactions of, 257. 

separation from copper, 257. 

ware, 256. 
Slag, 222. 
Slaked lime, 207. 
Slate rocks, 185. 
Smoke, 42. 
Snow-flakes, 63. 
Soaps, 200. 
Soda-ash, 200. 
Soda-water, 114, 200. 
Sodium, 199-201. 

carbonate, 199. 

chloride, 199. 

hydroxide, 200. 

reactions of, 201. 

theosulphate, 173. 
Solubility, 210. 
Solution, 58, 59, 
Spiral of elements, 266. 
Stalactite, 208. 
Stalagmite, 208. 
Starch-test, 149, 152. 
Steel, 224. 
Stibine, 235. 
Strontium, 210. 

reactions of, 211. 
Sublimation, 204. 
Substitution, 19. 

governed by valence, 189. 
Sugar, solubility of, 10. 

action with sulphuric acid, 11. 
Sulphates, 170. 

ways to make the, 172. 
Sulphides, 154. 

artificial, 157. 
Sulphur, 154-163. 

combustion of, 18, 67, 68. 



Sulphur, crystals of, 156. 

dioxide, 18, 163. 

effect of heat on, 155. 

flowers of, 155. 

group, 161. 

native, 154. 

preparation of, 154. 

roll, 155. 
Sulphuretted hydrogen, 159. 
Sulphuric acid, 166-170. 

action on copper, 163, 171. 

action on iron, 40. 

action on oxalic acid, 82. 

action on sugar, 11. 

action on water, 25. 

action on zinc, 170. 

manufacture of, 168. 

properties of, 166. 

test for, 167. 

uses of, 167. 
Sulphurous acid, 165. 
Sulphurous oxide, 163. 
Sulphur springs, 159. 
Supplies, chemical, 284. 
Symbols, 123. 
Synthesis, 24, 50. 

Table, blank, for the analytical 
groups, 269. 
of symbols and atomic weights, 

118. 
of French and English meas- 
ures, 286. 
of the periodic system in a 
spiral, 267. 
Temperature, rule to change Cen- 
tigrade to Fahrenheit degrees, 

287. 
rule to change Fahrenheit to 
Centigrade degrees, 287. 
Theory, 120. 



300 



INDEX. 



Theory, atomic, 123. 

Avogadro's, 122. 

distinguished from facts, 121. 

of matter, 121. 
Tin, 239-242. 

chlorides, 240. 

compounds of, 240. 

extraction of, 239. 

foil, 240. 

ore of, 239. 

properties of, 239. 

reactions of, 241. 

sulphides, 241. 

ware, 240. 
Tincture of iodine, 149. 
Tin-foil, 240. 
Tinstone, 239. 
Tin-ware, 240. 
Topaz, 233. 
Type-metal, 235. 

Unit of heat, 32. 

Valence, 188-191. 

a property of atoms, 188. 

denned, 189. 

described, 189. 

measured, 189. 

represented, 189. 

governs substitution, 189. 

governs reactions, 190= 

in classification, 189, 262. 

of boron, 190. 

variation in, 191. 
Ventilation, 80. 
Vermilion, 251. 
Vitriols, 166, 249. 
Volume, changed by heat, 71, 121. 

changed by pressure, 71, 121. 

composition by, 147. 

of ammonia, 90. 

of hydrochloric acid, 146. 



Volume, of nitrogen oxides, 147. 
of water, 56. 
the law deduced, 147. 

Water, 50-64. 

analysis of, 51. 

a product of combustion, 41. 

a product of respiration. 78. 

as a solvent, 58. 

boiling-point of, 61. 

composition of, 55, 56. 

distillation of, 60. 

drinking, 59. 

freezing-point of, 63. 

greatest density of, 62. 

hard and soft, 59. 

in the air, 74. 

in nature, 57. 

mineral, 59. 

of crystallization, 186. 

synthesis of, 31, 36. 
Weights, atomic, 118, 124. 

combining, 98. 

metric and English, 286. 

molecular, 125. 
White lead, 245. 
White vitriol, 214. 
Wrought-iron, 223. 

Zinc, 212-216. 

amalgamated, 26. 

chloride, 21, 214. 

compounds of, 214. 

group of metals, 215. 

manufacture of, 213. 

ores of, 212. 

reactions of, 214. 

sulphate, 170. 

sulphide, 161, 215. 

uses of, 213. 
Zincite, 212. 
Zinc white, 214. 



